I measured the girth of grip for a G21SF and a Sig 229. I used a tape (cloth type) measure around the upper part of the grips where the web of the hand would go and beneath the trigger guard where the middle finger would go.
The Sig 229 measured 7-3/8" and the G21SF 7-3/4". That's a lot of difference you think? Not really. That 3/8" difference represents less than a 7 percent difference. If we compare that difference to driving, and say we're going 60 mph, a 7% increase in speed would put us at 64 mph.