I am stuck between these two laptops. I am want them mostly for gaming but not for high end gaming. I want to play them on medium high settings with 30fps. I have seen benchmarks where the games play fine but never seen benchmarks with i5 with 645M.
Just going by the graphics card, notebookcheck.com seems to indicate that the 645m is a little bit stronger than the 7670m.
I couldn't find a comparison with the respective cpu's as well though. Technically, the i7632qm is stronger than the i5 3220m, I just don't know how much stronger. It really depends on what games you will end up playing, but I feel like the i7/7670m combo will be a little better. It will more battery so be prepared to be plugged in more. The i5 is much more power efficient.
Make sure you check the games you'll be playing for whether or not they are more cpu or gpu dependent as well.
I checked that 645M is way too powerful for 7670M. The benchmarks show that 645M is 10-20fps more better than 7670M sine ATI is always suffers from poor gaming archtecture compared to nvidia. i5 is stronger in terms of clock since it is 2.8ghz rather than 2.2ghz but i7 has 4 cores including 8 threads. Plus most games use 2 cores still.