Tim,
I have fairly large hands and the grips seem fine to me. I have two suggestions though.
1. I always wear riding gloves. My ventilated Summer gloves have gel pads built into the palms. My Winter gloves are well padded with insulation of course. If you don't currently wear riding gloves, you might find that they help.
2. For extended rides, you need some sort of throttle lock. You need to be able to relax your grip occasionally, or your hands will cramp no matter what size the handlebar grips are. On a long stretch, I will occassionally set the throttle lock and take my right hand off of the bars, swing it down by my side to get blood flow going & wiggle my fingers. Then I'll put my right hand back and do the same with my left hand. It helps a lot. Without a throttle lock, you can't do that with your right hand of course. Some folks have also tried the throttle rocker devices - mixed reactions to those, but they could also allow you to relax your right hand a bit.