when cruising in traffic about 55-60 what RPM's are best? between 5000-6000 or higher?
Define "best." :dunno:
I cruise in high gear for better mileage. I shift down a gear or two for more power if I need to get around someone.
It also depends on your gearing (sprockets), and tire sizes, and at 55mph you should be running 4500rpm on a stock bike. 4500rpm is the minimum I cruise in 6th gear.
For me, the fuel economy obviously is a factor, because up here the gas prices are horrendous.
When driving, I tend to go with the traffic flow. This leads to that if the road's clear, and there isn't much other traffic to be gotten around or (possibly) evaded, I'd be on the sixth (or any other high gear applicable to speed & load).
Then again, if traffic's heavier and there's lots of moving objects around me :o I may slip down to the fifth or downwards, so that I'm around 5k or slightly above; there's nice batch of power available from there on.
To your specific question, while cruising at 55-60mph I'd probably be on sixth or fifth, depending on the situation... so from the 4500 (I'm running stock GS) to 6k, probably not higher.
-Jarno