the difference in gaming isn't going to be much by changing out the processor. plus there is the risk that your laptop wont recognize it. its really a crap shoot. some have been able to use 1866 ram, some have not. your pretty safe with 1600 though if you dont already have it. you might not be able return the 5750m either if it dont works, so its up to you if you want to risk it and that money is worth the extra few frames per second you will gain.
what brand/model laptop is it?