I'm going to subdivide my response to my answer and my epic (yet hopefully informative/insightful rant)...
The short(isher) answer:
It all depends. win7 will make use of the hardware where xp didn't, and better than vista can, but it'll be your personal usage and system setup through program installs and startups that will rip a hole through your ram and show it to be insufficient.
If you do few things, you can up the aero glass eye candy and functionality with little performance degradation. But be reasonable with finding that medium and choosing your priority. The first stumbling blocks you will approach if your habits inflate are graphics and memory. Having crap open, having multiple things throwing crap at the same time, and lots of processes running is going to assert a footprint on ram. With aero and 2D gui effects hardware accelerated now, an inappropriate combo of usage and settings will result in latency, choppy navigation and program use, and weaker performance. Try adding the win7-based gui enhancements that have rolled down to xp and see how your system responds. Perform a clean install on the first partition on your drive. Place the pagefile on a separate drive. Or get some more ram. A reason someone on a laptop may be able to uber-multitask could be limitations on resolution and texture sizes. If you're using multiple or large monitors, mileage is going to relate differently.
Best advice I can think to give- take your time and be smart about things: don't install drivers with no release note mentions of win7-64 support, don't install core component drivers all at once or without restart, and let the predictive/preemptive caching and indexing take root before letting loose- like with a new car, you should let it warm up, don't excessively rev or apply throttle, and let things set into place. Otherwise you prolong the breakin and stress hardware. After adding lots of files- consider extending the time till the system sleeps to allow the index to build. With a large system change, rebuild the index.
With that quadcore, you will get good results with smp/core-parking. XP filled a core than started on the next, down the line. Vista tried to distribute and balance. Win7 assesses performance characteristics and will change affinity on the fly. I'm running F@H right now- it keeps it on the second core, because it's learned that starting a new task or one from idle is going to take cpu time from core 0. It used to more F@H over, now it just does it from the getgo. Take it easy on firefox- IE may not functionally appeal, but I admit it runs a lot better. Fingers crossed for natvie 64bit build of firefox.
Long(ererer) Response:
The only problem I see there is firefox open- 20 tabs or just a few. Since installing win7 almost a month ago, firefox will crash just checking my mail with no other programs running. Win7 is very good about releasing allocated ram when a program exits, allocating pagefile space to frequented tasks, and allocating cpu time. However, where you might have issues with flow and smooth working is with the the aero glass effects. If you have a lot of windows physically open (for the moment forget processes running) you might find your graphics card being stressed and lots of memory transactions occurring. I think this is because even the 2D effects are now hardware accelerated in windows- so the gui effects are more complex and cast a larger footprint on system resources.
It's a trade off- there's much to gain from moving from XP to windows 7 but you will find yourself either scaling back your usage/actions on the system, putting up with latency, or running in reduced functionality and eye-candy settings/modes.
xp won't tax your system, because the ability for it to utilize system resources is born and bred from older system requirements (single core cpu, 512mb-1gb ram, and DX 8/9 graphics running on cards with rendering pipelines and not cores, etc). It's like surfing the web, checking mail, listening to a library of music only as large as your ipod/whathaveyou can hold, and watching DVDs on a computer with a 1TB harddrive- you're never going to fill it up, or reap any benefits from the hardware other than feeling safe to see the pie chart of disk utilization always at a sliver. Vista was aimed at making use of the ever-increasing hardware availability and capability that went un/under used with XP, but did not do so optimally and intelligently+quickly enough. Vista had some ingenuity in its predictive and behavior learning capabilities but didn't seem able to enact them in a timely enough manner without befuddling itself. It was chasing the muddy dog around the house trying to wipe it with a single brawny paper towel while leaving mud tracks on top of the ones the dog left. Windows 7 can utilize hardware, does so smartly, and makes itself prepared to keep up and ongoingly adapt rather than play catch-up.
The problem with '64 bit' is twofold- native vs compatible, and availability. Some programs and drivers that worked on vista64 simply do not on win7 64bit. (at least pre-launch) the expediency of software releases to conform and uplift 64 bit capabilities is marginal at best. Which leads to the differentiation between native 64bit and capable/compatible; seen by peeking into the 'Windows' directory. Inside are three folders of relevance to the topic at hand: 'system' 'system32' and 'syswow64'. From what I've seen, complaining about multithreaded software being overdue is absolutely lost in the shadow of true 64bit software. Lots of the drivers and programs/update one might download come through clicking on a link with vista/win7_64bit_only as the title. Some of it involves a 64bit installer for a 32bit program to meet certification/installation/registry requirements on the 64bit OS. Others install a 32bit program that is run as 32bit (processes with ___*32 in task manager window). Then there are the 32bit programs that are kind of emulated to run as 64bit- they're not native, but if you only had an x64 cpu rather than x86-x64, it would run; with no additional access to resources or including capabilities than the 32bit program had to begin with. It seems that native 64bit virus/firewall/malware programs are just recently (uh, now?) becoming based on 64bit and then reduced to provide use on 32bit systems. Until now, it seems most software was ported from 32->64bit in a ground-up approach rather than meeting the more expansive need and then fitting to reduced needs of 32bit.
I'm hopeful a native 64bit firefox (unsure if Shiretoko simply up-bits the 32bit source code of firefox) would work smoother, and perhaps use memory more efficiently, if not use less due to more data per handle/thread carrying higher throughput rather than a whopping cache pool in memory being occupied to match the longer queue of instructions needed to do the same things in 32bit increments. I am infuriated when I go nuts and open a few firefox windows each with subject/category specific chains of tabs only to have it become unresponsive (in-program context menues, "File" and the like), slow to navigate to even google just because I have a bunch of loaded, idle tabs that are not even displayed on screen. Then, I finally finish waiting and successfully 'bookmark all tabs' in a window, and scale down to one firefox window with a modest amount of tabs open- and it's just as slow. Damn program can't access ram and cache hierarchies with the same expansiveness as a 64bit browser. 32bit addons for previous OS's only make matters worse. With things breaking into performance gains or a marginal standstill in 64 vs 32 bit, you're making a good decision not to shy away.
