I just got an 8700. I was never able to get used to the 7100 kayboard and Suretype. So the "nicer form-factor" really didn't help me because I never got used to Suretype. You miss a key on an 8700 and BlackBerry because BlsckBerry. You miss a key on the 7100 and it becomes Blsckwytart.
The 8700 keyboard does have smaller keys. Took me two days to get used to that (think Treo keyboard). For my money, the 8700 is great. And I also should have a 7103 from Verizon in next week to test.