Im building a system for someone and the budget is kinda of limited but he wants a 4870 with his kuma 7750 x2 . Do you guys think that the cpu will bottleneck the 4870 if so how bad? am i better off with a 4850 or should i get the 4870
Your pairing a low end cpu with a high end gpu, of course there will be some kind of bottleneck. I honestly feel my X2 7750 is some what of a bottle neck to my 4670 in some more cpu intense games. Left4Dead for example doesn't seem to care if I run the game 1680x1050 or 1280x800, I get an almost identical frame rate during intense battles.
I'm not sure if it will fit into the budget but, as suggested, the E5200 is faster than the X2 7750, especially when overclocked.
The HD 4850 isn't a huge power hog, and with a relatively normal system like the E5200 mentioned above you'll be fine with a quality 450W PSU. I used the PSU Calculator Lite v2.5 on an E5200 @ 3.0/1.3v/100% TDP, HD 4850, 2 sticks DDR2, 1 SATA, 1 DVD+-RW, and 2 120mm fans. The actual draw on a basic system like that should be about 280W unless you massively OC the CPU and GPU. The HD 4870 added about 20W. I haven't checked market prices in months, but the Corsair 450VX is a good PSU with plenty of amperage on the 12V rail.
If he goes with a E5200 system, then his only upgrade would be current s775 cpu's. Also the E5200 is expensive at $96. The 7750 is only $63.
If he goes with the 7750, he can upgrade to a Phenom 2 later on. If you overclock the 7750 to 3ghz, which will be very very easy, you'll be fine with your 4870, especially if your running at higher resolutions like 1680x1050 or higher.
Ok so i forgot to mention why i even considered a kuma 7750. My friend really wants a 4870 and not a 4850. I explained to him about 5200 as you guys mentioned and the 7750. Then things is in the long run like ZIPZOOMFLYHIGH said he could upgrade to a 720 BE but what about the 5200? He would have to buy a q6600 when he could get a 920 for just a few extra bucks right?. the monitor im getting him is a 22inch monitor.
WEll i conviced him to spend a little more and he is buying a p2 x3 720 just like mine. I think I made the right choice here because that way he can upgrade to a x4 if he wants to later without having to spend that much