Between those two, the 660 is better, but you're not looking at a level field here. The prices you listed here are horrible for these cards, not to mention, why does this site list the 7850 as 384 bit?. The 7850 can be found as low as $170, and the 660 for $220. If you're looking apples to apples on price, the 7870 is more on par then. When you pit (price-wise) the 7870 vs the 660, they trade blows in the games you listed. So then it's going to come down more to preference really. Overall the 7870 is more powerful in the all-around sense, but the 660 as some features the 7870 doesn't.
Edit: Actual dollar amount is for the states obviously. Seeing as the site is for an Australian store, the price gap for the two cards you listed is what I'm focusing on. The part about the 660 competing with the 7870, not the 7850 still stands. In some (few) cases though, the 7870 can even trade blows with the 660Ti.
See this is well balanced and your right about both cards..Either way you cant go wrong