For starters, I'm not sure the GS500's sprocket will fit. From what I could find on a quick search of an aftermarket sprocket maker, the GS500 does not use the same base # as the GSF600.
Secondly, a 6T drop out back would be a big change. Not only would you be giving up power wheelies (which most find difficult on the 600 already), but taking of from stops may involve a lot more clutch slippage.
Thirdly, you'd have to shorten the chain, so the only way to go back would be to buy another chain - or buy a shorter one for your 41T experiment.
You can go up to a 16T sprocket up front with only minor clearance grinding behind the cover. This would be about the same as a 3T drop in the back and can be accomplished without altering the chain length. Obviously, this means a 17T front is not possible, so further gearing changes to reduce cruise RPM would have to come from a smaller rear sprocket.