I'd say gtx650 ti boost but I would think about giving it a week or two b/c The 7850 2gs should lower in price and come with games that are a must buy. So value might be there.
The value of free games is a good point. Even if the GTX650Ti Boost offers slightly better performance, it's not the kind of difference that would provoke buyer's remorse. If you planned to buy those games anyway though, the cost savings could be significant.