I think the standard gearing is 15/44 S model with 108 link chain and
15/45 naked with 110 link chain.
Others wiser on here might be able to advise better but
i've got a 99 naked & changed to the standard last year & it seems fine.
check this site
http://www.gearingcommander.com// it tells you everything down to the smallest detail,you can play with the ratios & see the difference it makes