7770 vs 6790 vs 6850

http://www.tomshardware.com/reviews/gaming-graphics-car...

as you can see from this chart, the 6850 is one step higher than the other two. i would get the 6850

6850, but you need to make sure you power supply is capable of powering a 6850.

HD 7770 as you can see it outperforms a HD 6850

http://www.techpowerup.com/reviews/Sapphire/HD_7770_Vap...

they look nearly tied to me until it gets to extreme resolutions. if there was OC'd results from the 6850 that would help compare against the OC'd 7770. my 6850 is OC'd to 875Mhz and it made a huge difference from stock.

FSP PNR 550W. Is it enough for 6850?

My current card is Zotac 9800GTX+ and it works fine.

ye 550w is enough. The 7770 is a really good card and will use less power than the 6850, however the 6850 has a higher memory bandwidth so i would think in most games it will equal/outperform the 7770.

That Power Supply (having looked online) looks ok but im not familiar with the brand. Might want to have a look at the amps on its rail (rails) and make sure they are sufficient on the 12v rail for that card. Its 125 max tdp so 125/12 ~10 amps. you will need more than this available of course for the rest of the system, at least 35 in total i would say.

All of these cards are good but they're not a huge upgrade over your 9800GTX+.
You're probably going to see a 50% increase in FPS.

FSP is a pretty big PSU OEM, they just rarely sell under their own brand. Some Antec PSUs are made by FSP.
The quality of FSP PSUs in general isn't the best, but they're usually not terrible either.

Umm...wrong. As YOU can see, it does not. You can't cherry pick one game and say a card is better. Get real.

http://www.anandtech.com/bench/Product/536?vs=539

Well you haven't even told us what the rest of your system is but odds are a quality 400w would be fine.

it wasn't cherry picked you just have to look through all the Benches duh  

3 HDDs, 2x2GB ~1600MHz RAM, Athlon II x4 651, ASUS F1A75 Motherboard

Sakkura - Thanks for the info! I figured it probably wasnt a terrible PSU so I didnt want to give the standard response of "its not Antec/Seasonic/Corsair so its rubbish!"

actually just looked at the spec sheet and its very decent, so OP you should have no issue with the 6850 and this PSU

HD7770 and HD6850 are pretty much the same level..get whichever is cheaper..

Yeah that's what I posted. Maybe you should look and see.  

Thanks guys, I had to buy an HD7770 and it runs perfectly BF3 on Ultra in singleplayer but sucks in Skyrim and GTA4

OC your processor, Skyrim likes high cpu rates.