I agree with the above. If you're going between 660 and 7870 i would go with the 7870, and if you're going to spend that money you might as well pick up the 7870 XT since it's basically a slimmed down overclocked 7950.
http://www.amazon.co.uk/Club-3D-7870XTV ... 618&sr=8-4http://www.amazon.co.uk/Sapphire-11199- ... 618&sr=8-1The top one is budgetwise interesting since it's cheaper and you get Tomb Raider and Bioshock Infinite (Never Settle Reloaded). But the Sapphire runs cooler and quieter (the club3d i hear can be fairly noisy).
Talking about bang for buck i dont think you can beat the 7870XT at this time
This is an interesting review of the Club3D (written in Dutch but you can view the benchmarks and scroll down to click the games you want to see), interesting because they compare the cards on triple screen resolution as well:
http://nl.hardware.info/reviews/3690/8/ ... tlefield-3Performance wise the Sapphire should perform basically the same, either wipes the floor with a 660(Ti too).