Stick with a 17 or 18 tooth sprocket for two up riding. I use a 17 tooth. As it is, my top speed is the same in 4th. and 5th. gear (110MPH) indicated. Wind resistance limits the top speed in fifth gear. I weigh 230 lbs. With a 19 tooth sprocket fifth gear would be wimpy and not as useful for me. I do not even use fifth gear for spirited riding.
Buy the Speedmaster, you will never regret it. Now is the time to buy a leftover 2006. Check Life Cycle in Kazoo also, they have some leftovers on their website right now. You can get out to the door, tax included for the sticker price when there is snow on the ground.
Good luck.
