Hi , I'm thinking of getting a mid-high level GPU to play games, and help in photo and video editing. I don't really want to spend to much , but if its money well spent, and something that will be more "future proof" , then so be it.
Then there's the 670 , which ( I was basing this on that fact that a 660Ti was £250 ) was a little bit more , at £300 , which has that bigger memory bus [ not sure how much of a difference this makes ] and is about 10-25 FPS better than a 660Ti.
the 570 is horse manure next to the standard 660. the 660ti is over priced for the small amount of performance over the standard version. So either a 660 non ti or a 670........... with either the 660 or 660ti you may have to make concessions at higher settings in some games because of the small memory bus.
Since the rest of your build is solid, you could get away with the 660 for acceptable frame rates in most games. However, if you are after serious performance and want to be more "future proof" then get the 670.
(By that I mean that you are more likely to skip a generation if you get a good card now. This can save money in the long run and give you better performance. I have seen far too many people go 460-> 560 -> 660 when they could have gone 470 -> 670 for the same price. I hope this helps)