Ok so I am primarily looking at playing modern games (especially the upcoming BF4) So at this minute I am looking at a Radeon HD 7870 OC SAPPHIRE ( http://www.newegg.com/Product/Product.aspx?Item=N82E168... )
The CPU I will be using is the Phenom II 965 quad core 3.4 GHz (probably overclock to 3.8-4), Ram: G.Skill 8 Gb (2x4) 1866 DDR3, and a ASUS M5A97 R2.0 AM3+. So the question is would this set-up run nicely (45+ fps at lowest)? Is it worth upgrading to 7950? And if so which one? OR, would it be best to go with 660 ti? Would i need a different MOBO? thanks for any advise!
Would your PC with the 7870 play the games on Ultra at 45+ FPS? Probably.
7870 in and of itself is a decent card and should be able to push ultra settings without too much difficulty. Certainly 30 FPS would be doable and probably 45+, depends on the AA.
Is it worth it to upgrade to a 7950? Probably. You'll get more vram but a lower core clock, so toss up really. The 7950 will tackle the Ultra settings better, between the vram and the bus width, and allow for more AA while still keeping higher framerates.
Can't really comment on the 660ti, though my understanding is it is slightly better than a 7870 but has trouble once you start increasing AA. 7950 is better than 660ti.
You would not need to change your mobo to use any of them.
I will recommend you to upgrade your CPU as it is surely bottlenecking your graphics card, I had a phenom 965 overclocked to 4 ghz and was bottlenecking my 660 ti, on Far cry 3 for example in some cpu heavy scenes my card was being used 60% and i was getting like 35 fps, while in some others 80% etc.
Now i have upgraded to a 3570K and my gpu is always being used 100%, i couldnt believe I was getting constant 60 FPS+ in far cry 3, and in all games in general the performance has improved a lot including crysis 3.