After a couple of month, some upgrades, finally I changed from F900BT (V3.01) to F10BT (V1.00). 
I must say it is a total different world.
What are the pros/cons:
+ bigger screen
+ much faster screen response, very quick
+ button are bigger, much easier to hit
+ boot time much faster (7 secs music from radio, 15 secs from SD, screen ready after 15 secs)
+ iPhone connection no problem
+ Voice volume control (Navi and phone) much better
+ while phone call, you are able to fully operate the unit
+ sound quality much better
+ more features like eq and sounds enviroments (DSPs)
+ navigation much bigger screens, easier to read, not so much details
+ no errors so far, works fine
- more expensive
Thats the way it should be.
I'm glad I made the step. 
Get a first impression of the unit here:
http://www.youtube.com/watch?v=3CAj7VbgEZU
I will give some more information after more tests.
Swissguy01