I made the switch from the 8700 to my 8300 and haven't had a days regret! There will be minimal, if any transition period from the side track wheel of your 8700 to the center track ball (although it's more of a clicking toggle than a rolling ball).
I've used a variety of PDA's and this unit is simply amazing in it's UI, I've never had it crash and only early on had to do a battery pull due to memory leakage. You will want to buy an micro sd card for ringtones, pictures and video- An micro SD and following John Clarks memory optimizer http://www.blackberryforums.com/gene...ee-memory.html
and you will be memory happy.