I strongly disagree with the stuff about quads, because in most daily use a higher-clocked dual core with more cache per core is going to feel snappier than a quad-core with cut-down cache that can't clock as high.
And I have both an E4300 and E8400 (well the xeon version), and even at the SAME clocks the E8400 feels much snappier in real-world usage. Yes, I know there were tweaks to wolfdale, but they're less significant than the cache bump, and I believe that even if I clocked the E4300 slightly higher it would still feel less snappy in daily use.
The benchmarks might show 20% or 15% or 10% or whatever difference, but that's averaging all the frames together. The truth is that some calls to the CPU will be MUCH faster, while some will run at the same speed (since it fits in the cache) and it AVERAGES out to 20%.
You have to realize that on the slow parts you'll be screaming murder because your computer will feel much slower than one with more cache. Looking at averages is silly because as long as it's "fast enough" it'll feel fine, it's the parts where it's not fast enough that you'll notice. The average hit in speed in an app might be 15%, but that means a lot of parts run at the same speed while some parts run like 40% slower while it has to hunt through RAM for the data because it's not in cache.
Judging how fast a CPU is based on the average FPS or average performance of an app on benchmarks is just not reflective of REAL WORLD performance, where the larger cache will FEEL much faster in use because it's not hitting slow-points. If Unreal Tournament 3 runs 20% slower on average that means there's parts where it's going to be 40% slower because the CPU is trying to do a whole buncha stuff it can't fit in cache, whereas there'll also be parts where it's running 95% or 100%. You might average it out to look at benchmarks but when you're playing the game and it tanks to 5FPS because a buncha people just fancy guns at you it's going to feel a hell of a lot more than 20% slower than the E8400.
BTW OP, if your budget is $800 you can EASILY afford the E8400 if you shop around. Video cards are very cheap now, RAM is very cheap now, go look at the hot deals forum, so as long as you don't want a particularly fancy monitor you should be able to build a good system.
And while the E7x00 series is cheaper the jump from 2MB to 3MB still isn't as awesome as getting the full 6MB intel figured was optimal. The whole reason they increased from 4MB to 6MB was because 4MB still hit slowdowns.
You don't have to believe me, if you have a friend with a 6MB cache system go use their system, and then go use a system with 2MB of cache. Run the apps you actually run, etc.
The way I look at the value here is that the 6MB cache CPU will make your system run about 15-20% faster. 20% of $800 is $160 man, and you're not saving $160 by buying the cheaper CPU, so it's really not worth it. This isn't even considering the fact that the slowest parts are going to be more than 20% slower and those are the parts that count (since the stuff that runs fast on both CPUs probably runs fast on almost any CPU anyway and wouldn't feel slow on any system).
I dunno what video card you were planning on using, but the 4850 or even 4870 can be had very cheaply nowadays-$125 after a rebate for the 4870 and cheaper for the 4850. Or you can go 4830 and overclock it, you can get one for like $80 at newegg ($90 if you're too lazy to do a rebate).
Unlike the GPU the CPU is used 100% of the time (ok well, the GPU is used 100% of the time but the 2D really doesn't matter), so you'll feel it being faster or slower 100% of the time. I'm not saying you should go buy the most ripped off CPU in the world, but as long as the performance change still makes sense in relationship to the cost of your system I think it's worth it.
The same logic is why quad-cores aren't always worth it, since most apps simply can't use all 4 cores and most quad-cores cannot overclock as high. And if you DO want to overclock as high you have to invest extra $$$ in better cooling because trying to run a quad-core at 4Ghz takes a lot more money in cooling than running a dual-core at 4Ghz (also, you need a lot of luck if you wanna hit 4Ghz on a cheap quad).
In the real world an E8400 clocked at 3.8Ghz will feel faster about 98% of the time versus something like a Q9300, because it'll be clocked faster AND have more cache per core. Sure the Q9300 will feel faster if you're encoding a video, or if you're lucky enough to play a game that happens to use all 4 cores correctly. But the other 98% of the time your system will feel slower, so it makes no sense to me to go quad unless you know you'll be using programs that actually use 4 cores. And even in those programs the E8400 will make up some of the performance gap with it's higher clocks.
Some real world benches with apps people often run:
http://www.tomshardware.com/ch...-Professional,825.html
http://www.tomshardware.com/ch...3-2008/iTunes,827.html
http://www.tomshardware.com/ch...hotoshop-CS-3,826.html
As you can tell in the real-world quad cores don't mean much...only the extremes can beat the E8400 here (and overclocking the E8400 easily gives you the best performance)
Look at where the E7200 is on those charts and realize that the E5200 is even more cache-starved-you're looking at a HUGE performance hit in very commonly used programs. And that's just the average hit, imagine the parts where the hit is even worse.
Synthetic benchmarks where they actually use all 4 cores just don't reflect real-world usage. The only apps where you'll notice real-world benefits are encoding/rendering type apps.
I know the way I use my computer my system is probably running all those programs way faster than anybody with a budget quad-core, and it's probably faster than most expensive quad cores as well since it overclocks better. The E8400 is just a really sweet processor for people who want TOP NOTCH performance in programs for the lowest price. The E8600 sitting on the very top of the Photoshop chart is just a higher clocked E8400, and it's 2nd on the iTunes chart, and 3rd on the Acrobat chart. All the other CPUs in that territory are $1000+!!!
Obviously if you're seriously limited by budget the E5200 is a good choice, but if you use your computer for the apps that most people run an overclocked E8400 hangs with $1500 CPUs. Which is why I think it's a killer value even though the CPU costs 2x as much as the E5200.