Been running skyrim on this machine since it came out with no problems. Settings set on medium to high quality. Loading it on Sunday I had piss-poor performance. 3-5 minutes to load zones and shuttering lag issues. A system restore ended up fixing my problem but now the lag is back again. All video drivers are up to date.

XPS 1645
6gb Ram
Radeon HD 5730
i7-720QM, 1.6
Win 7x64

Your BASE core speed is not what counts for games, at all, unless you accidentally changed from performance selected to appearance selected, or some other power level setting is changed, so you are no longer having the i7 accelerate to its Turbo speeds.