PII X3 720 + HD 4850 or X2 7750 + HD 4870

go with combo 2, then upgrade to a Phenom II 955 when you think you need to, and you might want to pay the little extra for the 1GB 4870 if playing at 1920x1200 with AA on

and no, the 7750 will not bottleneck the graphics card, especially when OC'd to 3GHz (or 3.2)

I would go with the PII 720, combined with an AM3 board. This will give you more upgrade possibilities.

What resolution will you be playing at? The 4850 will be fine for COD4 etc at lower resolutions.

The 720 is a far stronger cpu than the kuma .

Id go with that , and the 4850 . Its easier to upgrade a gfx card in the future if you need to .

I'd go with a 720 4850 setup. Since you're not playing games that are too demanding right now you can just update your GPU latter on and you're overclocked 720 will probably help you keep pace. I figure you probably won't really need a new GPU until the second gen of DX11 cards are out. It's up to you of course.

Either way if you're going to overclock I recommend getting a good aftermarket cooler, especially if you go with the 7750. You can overclock the 7750 with the stock cooler, but I wouldn't really recommend it. At the least use some good thermal compound like arctic silver.

+1 X3 720 and HD4850. For me, I think the boost from the X2 to the faster X3 would be greater than the jump from 4850 to 4870.

Again +1 for the X3 and the 4850...the all round performance will be better than the 7750+4870...

I'd also choose the X3 720 and HD4850.

I'd also get a Crossfire motherboard and toss in a second HD4850 when they become dirt cheap (like $60) as long as your PSU supports it (not just power but the proper connectors, though most have the 2x 6-pin two cards would require). It's worth spending a bit extra on a solid PSU like PC Power & Cooling Silencer 750. Corsair is good too. You can get away with cheaper PSU's but you take your chances. There are sales too.

COD4 plays pretty good on my X2-4800+ and HD3870 so you'll be pretty happy with the HD4850. Games like Starcraft 2 and Diablo 3 will look awesome with that system.

Make sure to get 4GB of RAM.

The stock CPU HSF is probably pretty noisy. Most people prefer installing one with a 120mm fan like the OCZ Vanquisher. That CPU fan should be hooked up to the CPU fan motherboard connector with the BIOS fan speed control enabled. You should also have a second, low-flow (low CFM and low noise) to move case heat, don't rely on your PSU and graphics card to do this. I bought one and it has 4-pins and is not compatible with my motherboard. Live and learn. Aim for 17dBA or lower on the single 120mm rear fan like the Thermalright Stealth Silent 120MM FDB Case Fan 1000PRM 38.9CFM 15.8DBA. Confirm pin support. There may be standard MOLEX adapters too.

Since you are building a system now, I recommend getting a copy of Windows 7 RC 64bit on May 5th for free, then get an OEM version when it comes out.

Thanks for your replies. I'll go with the X3 720 + HD 4850. I am also getting the Sunbeam CR-CCTF92-4 92mm aftermarket cooler for overclocking. For PSU, I've picked out the Tuniq Potency 550W. Is that a good choice? I chose it because it is rated 80+ efficiency and has 3 good reviews so far... and it's only $40 after rebate.

Thanks again for your help.  

Have you found any competent technical reviews of that PSU, e.g. on jonnyguru, hardocp, or hardwaresecrets?
That PSU IS listed at www.80plus.org. You can at least be reasonably sure it won't choke at only 75% of its rated output, since presumably it was tested all the way up to 100% load, although that doesn't say anything about the quality (i.e. ripple and noise) of the output.

AnandTech had a Tuniq Potency 550W on the test bench. It had quite a bit of ripple and failed the stress testing.
"Unfortunately, the Sunbeam Tuniq Prophecy didn't survive our burn-in test. It self-destructed under full load at 40°C, so we definitely wouldn't recommend that power supply unless you live in a cold environment or only plan to run at lower loads. All of the other units survived heat conditions of 50°C"

from: 500W to 550W: 12 Power Supplies Compared
http://www.anandtech.com/casecoolingpsus/showdoc.aspx?i...

Hm... looks like maybe the Tuniq isn't a good choice then. My other option was the OCZ Fatal1ty 550W. Just $10 more after rebate. Is that the best choice in this price range? I don't want to go above $50 after rebate for the PSU unless strongly advised. Any other suggested PSUs in this price range?

Also, another question, should I wait on the Radeon HD 4770 instead of getting the 4850? It looks like it might be just about the same performance and cheaper. What do you think? With the 4770, I could go with a lower PSU right? Like a Corsair 400cx?

Based on a variety of benchmarks, there is a much large increase in gaming performance for the x3 720 over the x2 7750, more so than the difference between a 4850 and 4870. What is important though is the price difference, a x3 720 is on average $80 more whereas the difference between a 4850 and 4870 is around $50. Look up the benchmarks and determine for yourself which price difference is worth the performance.

I've looked up some benchmarks from different sites and it looks like the x3 720 + 4850 outperforms the x2 7750 + 4870. So I'll stick with that - and it is true that the video card can be upgraded later easily if needed. Thanks for all of your help.  

Yup, simply swap it the old card out for the new, as long as the new card is compatible with your mobo (assuming that years from now PCI-e is replaced with some new standard, but most likely by then you'll be ready to build a new rig anyway).

If you start out with an ATI card and then switch to an Nvidia card then you'll have to uninstall the old ATI drivers and then install the new Nvidia ones.