The GT 650m is a good card and the i5 will not be a bottleneck with it. I don't think it's worth going for the i7. The i5 can do all you will need and with less power which helps it be the portable laptop it always wanted to be
There are reviews out there on the M14x. I Googled one for you with the GT 650m. It's running the i7 but the CPU is not really what matters when gaming, it's the GPU.