Lemme clear up some fog regarding this. According to techpowerup (they don't "guess" as much as Notebookcheck.com seems to) the 650M is 45W TDP, and the 660M 50W. That being said, the 760M is not equivalent to the 660M. The 660M is the exact same chip and setup as the 650M but overclocked. This years version of the 660M is the 755M. The 750M has a TDP of 50W, and the 755M has a TDP of ~50W (maybe 52W, but it's only overclocked slightly).
Directly following those chips is the 760M which is a completely different chip. The 650M, 660M, 750M, and 755M (refreshed chips for 2013) are all essentially the same chip and set up, slightly different memory clocks, but that's it. The 760M is a more significant jump in performance of about 20-35% in some games frame-rates, whereas the 750M/755M would only be a bump of maybe ~10-15% from the 650/660M. The TDP of the 760M is 55W (according to techpowerup). The 765M that the razer has is a whopping 75W though, and has a completely different bus interface so it is likely way out of the question for the rMBP. The 765M would be a massive improvement in graphics, seeing an increase of about 40-60%.
My concern with the 760M not being a viable option is because obviously TDP isn't the only determinant of whether a laptop can "handle" the dispersion of heat from a chip, and the 750M/755M have 1300 million transistors, while the 760M (being a completely different chip) has 2540 million. I think more transistors means more heat.
EDIT:
Also, the 770M is a 765M with faster, and more memory as well as a modified clock speed. It is also ~75W like the 765M.
Then after that is the massive 780M chip which you see in the brick computers gamers use with 1-2 hours battery life, and it has ~100-125W TDP