They trade blows depending on the game tested. If you have a lower budget and want free games, get the 7870 xt but if you have a higher budget and prefer nvidia for its features such as physx or FXAA, get the 660 ti.
Yes please change to 64 bit because 32 bit can only use around 3.5 gb of your 4 gb if you stick with 32 bit. ( I sadly bought 32 bit windows so I can only use 3.5 gb of my ram XD)
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What is your budget?
Where will you buy it?(newegg.com, a retail store, etc.)
What are your other specs? (namely psu, cpu, mobo, ram)
What is your screen resolution:
I'd say buy the 7850 and the 4gb of ram then just save enough money for another 4gb of ram so you can get a 7850 and 8 gb of ram. Otherwise, 4gb of ram is fine for gaming.
GTX 780 in a 3 way sli will beat the titan 2 way sli and will also have a better price/performance ratio. I don't know if nvidia will update their cards to support dx12 but i don't think they will.
Powercolor's 7990 uses a lot more power, produces a lot more heat, takes up 3 expansion slots, is a lot more noisy and needs a push of a button to activate the boost function.
AMD's reference 7990 uses less power, produces less heat, takes up only 2 expansion slots. is quiet and has higher...
Lol my old pentium 4 2.4 ghz with 1 gb of ram choked on 720p, that thing wont play hd videos even with a new gfx card which will be hard to find because that mobo still uses agp.
I tried my best to stay within budget
CPU: http://www.newegg.com/Product/Product.aspx?Item=N82E16819116405 $69.99
CPU cooler: stock
Mobo: http://www.newegg.com/Product/Product.aspx?Item=N82E16813131888 $59.99
Storage: http://www.newegg.com/Product/Product.aspx?Item=N82E16822148767 $59.99
Video...
Lack, do you mean the wattage of the PSU not the voltage? Anyway, among those listed the 6570 is the best. Get a 6670 if you can afford it cause it is much better than any of the cards listed.