Why would you say that it is better?
The 7850 runs faster overall compared to 650 ti, look through this review http://www.anandtech.com/show/6359/the-nvidia-geforce-gtx-650-ti-review/10
basically in every benchmark the 7850 1gb comes out on top. Sometimes it may be a 2fps difference but other times It can go up to 15fps difference.
If you want higher performance then go for the 7850 its only a $5 difference.
Edit: The 7850 can also be oc'ed more effectively then the 650 ti meaning you can get even more bang for your buck!