I have read of others doing this with a G74 and being successful, but the G74 is not designed for the TDP=55Watt CPUs. You will stress the cooling system, and your processor will likely throttle back alot, and/or turbo won't even kick in when you need it because of no thermal headroom. In short it will be like having a gimped 2960XM,not something you want to spend $500+ on. Advice: get a 2860QM or another top-end 45W i7 mobile. It will work like it should.
It won't be a massive gain in performance (not like dropping in an SSD would, for example), but will be as fast as you can go in a G74, if thats your goal.