I wouldn't use either of them because you're going to need more than 1GB of VRAM. I wouldn't get any card that is an HD 7850 or lower with less than 2GB and the GTX 650 Ti is DEFINITELY lower. As for the pricing, this just shows how arrogant nVidia is. The Radeon HD 7850 absolutely ROASTS the GTX 650 Ti by 30% when both are at stock speeds, nevermind when it's overclocked. Check out these gaming comparisons from AnandTech, you'll see that a Radeon HD 7850 even beats the GTX 650 Ti Boost in most games, never mind a normal GTX 650 Ti:
Dirt: Showdown:
GTX 650 Ti Boost - 61fps avg.
HD 7850 - 73fps avg.
http://www.anandtech.com/show/6838/nvidia-geforce-gtx-650-ti-boost-review-/3
Total War Shogun:
GTX 650 Ti Boost - 56fps avg,
HD 7850 - 55fps avg.
http://www.anandtech.com/show/6838/nvidia-geforce-gtx-650-ti-boost-review-/4
Hitman: Absolution:
GTX 650 Ti Boost - 53fps avg,
HD 7850 - 59fps avg.
http://www.anandtech.com/show/6838/nvidia-geforce-gtx-650-ti-boost-review-/5
Sleeping Dogs:
GTX 650 Ti Boost - 54fps avg,
HD 7850 - 58fps avg.
http://www.anandtech.com/show/6838/nvidia-geforce-gtx-650-ti-boost-review-/6
Crysis: Warhead:
GTX 650 Ti Boost - 40fps avg,
HD 7850 - 44fps avg.
http://www.anandtech.com/show/6838/nvidia-geforce-gtx-650-ti-boost-review-/7
Far Cry 3:
GTX 650 Ti Boost - 51fps avg,
HD 7850 - 53fps avg.
http://www.anandtech.com/show/6838/nvidia-geforce-gtx-650-ti-boost-review-/8
Battlefield 3:
GTX 650 Ti Boost - 70fps avg,
HD 7850 - 61fps avg.
www.anandtech.com/show/6838/nvidia-geforce-gtx-650-ti-boost-review-/9
Civilization V:
GTX 650 Ti Boost - 56fps avg,
HD 7850 - 58fps avg.
www.anandtech.com/show/6838/nvidia-geforce-gtx-650-ti-boost-review-/10
So, the GTX 650 Ti without boost isn't even in the same league as the HD 7850 and yet it costs $20 MORE?! I think we both know what you must do.
Man, this took a LONG time to write, but if it gets best answer, it was worth it. Cheers!