I currently have an AMD Athlon 4400+ CPU. Does anyone have a Radeon 4850 paired up with a similar CPU of this type? If so, ho does the 4850 perform with it? I am considering buying the 4850, but don't know if it's worth it. I currently have a 8800GTS 320.
i have an athlon X2 4200+ with a 4850, and while the cpu is probably holding the gpu back, i still get great performance. plus if you have a chip with the G2 stepping you could overclock it to around 2.9Ghz, maybe more. i've only gotten mine up to 2.9. by the way, im currently running at the stock 2.2Ghz.
I'm assuming that this is the 939 socket 4400+ CPU. I have one in a business computer, which used to be a gaming computer. I think the a 4850 would work well with it, especially if you have the 4400+ overclocked. I have a 8800 GTS 640 in my 4400+ machine, so have a similar card to your 320 version. Toms has a guideline for upgrades, with a recommendation of three steps or higher for noticeable improvement
Unless you're playing an RTS, you should be fine with that processor. It isn't going to "severely" hold back your card like some people try to make it out like it will. It's not like pairing a 64 X2 with a high-end card is going to suddenly halve the graphical power of the card. You'll just be framerate capped by your CPU instead of your GPU at lower resolutions, but that's common even with incredibly fast CPUs.
All this means is that you might have a maximum FPS of 90 in a game, whereas a QX9770 might have a max FPS of 130. The only time you might notice your CPU actually limiting noticeable performance in a game is when you play RTS like SupCom with 2958239572385 units or do something very physics extensive, ie. driving into a house in Crysis and destroying it. You might see slight framerate drops, but that's mostly with single-core CPUs. My 6000+ does just fine.