If you want to see what your cpu is capable of (it's bottleneck), lower the resolution to 640x640 in your favorite game (half life 2, doom3 are good choices) and run a benchmark.
Lets say you get something like 75 average frames per second in doom3. That's your starting point and is most likely your CPU bottleneck for that game.
Now, increase the resolution to 1280x1024 or whatever resolution you usually play at. If your CPU is the bottleneck, your FPS will stay at around 75fps. If your video card is the bottleneck (like I suspect it is), your FPS will go down - say to something like 40fps. If your video card was faster, it should have been able to reproduce the higher-resolution benchmark at 75fps, just like it did at 640x480.
Your cpu/video/resolution bottleneck will vary by game, so there's no good answer for "what's the best card for my system".
To understand this better, you need to know that a CPU in games really only handles AI, geometry, and various other things not related to video output. The GPU handles each individual pixel on the screen, lighting effects, aa/af, textures, shading, and basically most everything you see as output. When you increase the resolution and most video settings, you put more stress on the GPU and little to no stress on the CPU.
So at 640x480, your video card needs to render 307,200 pixels for each frame.
At 1280x1024, it needs to render 1,310,770 - this is 4 times the work, so it can potentially be 4 times slower.
Here's a real-live example of how you might want to go about matching a video card to your system.
I had an AXP system clocked at 2200mhz with a geforce4 video card. At the lowest resolutions and quality settings, I could get around 55fps in a doom3 timedemo. But I want to play at 1600x1200 with 4xaa at about the same speed (the geforce4 gets less than 2fps at this resolution).
So, I know that my CPU is capable of running doom3 at 55fps, so I go out and look for a video card that can run doom3 at 1600x1200 at around 55fps.
Here we go!
http://www.anandtech.com/video/showdoc.aspx?i=2552&p=10
At the resolution I'm looking for I find that these cards are capable of this:
6800gt - 45fps
7800gt - 51fps
7800gtx - 60fps
The scores are quite close, so I look for the cheapest card. I'm also limited by AGP. I choose the 6800gt and find a good deal for one for $220 used.
There ya go - a good match for an xp 2200mhz and doom3 at 1600x1200 = 6800gt.
As you can also see, that's about the fastest and most expensive video card I could possibly get for an amd xp system - This is almost always the case with games since at high resolutions, they're all video-card limited.
One final example - my A64 running at around 2500mhz, gets around 100fps in doom3 at low resolution. I'd need a SLI'd GTX system to properly match with it if I wanted to play high resolution at 100fps.
Sorry, I was sitting around with nothing much else to do. Maybe one day I'll compile a cpu-bottlenecking chart by game and put it up somewhere.
Facebook
Twitter