I have a 6 for around here (almost 4000 ft) and a 8 for the coast, if I could only have 1, it would be the 6. the 8 has too much grip and you really have to have a bike set up to rev and ride it hard to get the 8 to work good, the 6 allows you to pick the throttle back up if you have to let off. a 8 might work better with the gearing the Dave suggested, all my experience is with 14-48 gears.
thanks to all! I'm running a 13/50 set up. think I'll go with the 6 paddle. now to the net to find the best price. wish I could fine a spare rear rim assemble so I could just put it on and leave it on.