IMO if you go from a 750 to a 650 and it makes it more peppy than the 750 was just to much. Since it worked for TOD it may work for you. I had tried a 650 on mine and the 750 was alot more responsive. It all depends on what your engine likes. If you have access(friends etc) to one of each, try them and see which one works better. I may have had more compression and more flow than what you have.
By the way TOD, I like the avatar.