I replaced my 5" OEM grips with 4 1/2" grips and found that my hand seemed to cramp up a lot. Soon after I switched back to a new 5" set and I'm happy again. I'm also using stock Honda bars which locate the controls and didn't care for the 1/2" that the bars extended beyond the grip end. I suppose if I had liked the 4.5s I could have cut the bar shorter though...
(75 cb750 with 400F bars)