I am still in the shopping mode so I don't actually own any of these yet but I must say I am bummed with the X910bt. The F910bt has the Premier logo on the front, The x series of the same name doesn't. OK I admit it is a really small thing. Back in the day, the Premier logo really meant something (kinda like the Sony ES logo means better quality over hte non ES line). I am saying this mostly toungue in cheek.
As a side note...
I have an opportunity to get an Eclipse 62dbt, Basically the 6620 with the bluetooth otpion. I can get this unit for $500 nib. I can get the x910 for $550 NIB... Not sure which one to go for. The eclipse will be a MUCH better sounding unit, but it looks a little dated. I don't care for the add-on Blue tooth too. The GPS is kinda dated looking too. The 910 can be modded so if I don't like the look of the nav I can skinn it.
The 910 has built in BT as well as a much better look. The maps will continue to be updated (Eclipse has said they are stopping making maps past next year.
What is the deal with the IPhone GPS feature, where you can transfer a destination form your phone directly to your 910 (or the 710 if you have that one). Does it work well?