Tenvis :
The 7850 costs 195$ while the 650 Ti Boost SC costs 196$
... Where exactly are you buying from? Those prices sound kinda ridiculous for those cards nowadays.
Anyway, if it's a 1GB 650 TI, then the 7850 will be a better choice thanks to the larger frame buffer. The 2GB version usually on par with the 7850, and at other times is a little bit faster or slower, though it really depends on the game itself.
Also, AMD's been kicking microstutter in the balls with their more recent drivers from what I've seen. Some games still have their issues, but that can be said with both companies.