I have the very same issue with my 9900 ... my sensitivity is at 80% .....anything lower irritates me because it moves too slow to my liking. I'm yet to upgrade to any OS update that seems to fix the problem. I've been living with it for the past 2 months and it doesn't get on my nerves as much anymore ...... and as for the sunlight brightness issue ....
I'll be updating to OS 7.1.0.523 though .... AW JM above seems to not be experiencing the problem anymore it seems