First of all I am not a AMD fanboy I hate AMD's drivers! I have a R9 270 in my new i5 3470 Rig because I could not pass up the price performance, But I do still have my beloved GTX 650 Ti I keep in my old i5 750 Rig.
But as far as the 750 Ti being faster than the 7850? This is news to me LOL, The 750 Ti does not out perform the 7850, It may do better in Nvidia games by a few FPS like in Bioshock Infinite, And a couple of other titles. But in almost every game the 7850 is going to beat the 750 Ti especially when resolution and AAA come into play, The 7850 has a decent memory bandwidth of over 150GB/s while the 750 Ti has only 86.4GB/s of memory bandwidth, This means the 7850 can fully use all it's 2GB of V-Ram And the 750 Ti can't fully use all it's 2gb of V-Ram. This means the 7850 can handle higher AAA settings as well as beat it in FPS most of the time. So if you find a 7850 for a decent price go for it, But the R7 265 is only $140 and is now cheaper than the 750 Ti, And the R7 265 is a more powerful version of the 7850 with a even faster memory bandwidth of 179.2GB/s. So your best bet is to get the R7 265, But you can now find some R9 270's for $150. I know some will say but some people have low watt PSU's, First of all if your rig's PSU can't handle a 150watt TDP card then you should not be gaming anyway. If you have a PSU that cheap then it's only a matter of time before it blows under stress of gaming.