IMO, raising the final ratio,...anything short of more gears, will spread the 5 gears farther apart, and you will be slower thru the gears than you are now.
I don't have a tach yet, but it sure sounds like the engine is not tach'd out at its top speed...85-90 in 5th gear, so any higher final ratio (or higher gear) will only hurt you up there.
Cruising at 60, a higher gear mite be more comfortable,.....if it didn't turn the exhaust pipe bluer than it already is.
For my riding, the s-40 is geared perfect.