1200 sporty sprockets

ive searched a bit with little results to the specific questions im asking. doing the math has worked but the results have been less that desireable. looking to find out for those of you who run a 1200 evo sporty motor with 16 rear and 21 front what the best combo you found gives you the least vibes and lowest rpms at 70+ mph. i want to have a decent freeway bike so i can take longer trips.my bike is a buell 1203 motor in a paugcho frame with a 21 front and 16 rear with a 48 rear wheel sprocket and 23 tooth front sprocket. chain of course. as of right now it feel like a 20 minute ride at 70 will either shake the bike apart or blow the motor.