although the 2630 is rated at stock of 2.00ghz it will actualy turbo up to 2.9 so should handle most games adiquately. it will struggle on games like bad company 2 that need a 2.4quad or better as the turbo doesn't oc all 4 cores
the 720qm is even worse off in that its only rated at 1.6 but both have very good mobile gfx solutions. the 5870 being slighlty better. but the slower cpu means both systems will perform prety equally a lot of games.
persoanlly i would go for the 1 with the fastes stock cpu as theses very little in the gfx. maybe you can find an even faster stock cpu on another model... preferably 1 of 2.4ghz.