As Tharos suggested:
1. Roll rate is TAS dependant, make sure your airspeed is near optimal one
2. Max. roll rate as listed in "sustained" one, this means, after you already roll with the fastest possible angular speed. But if you start from level flight, you have to angularly-accelerate to full speed, which can take twice as much time.
there is more then just vegas, I use vegas only for editing, and for me vegas and also other editing programs(avid, premiere,...) are not made for effects.
Try some compositing programs and you can do everything you want.