40 tooth bottom is way to go. I did that on my 07 Attak. Made a huge difference. Lost a few mph on top under perfect conditions, but gets up to speed much faster. The 40 tooth reverse gear is more expensive than a top gear, but still cheaper than a top gear and 68 link chain. Also rolls easier.
If you buy the 40 tooth gear from Yamaha, you might as well get a new bearing for it as well. No sense trying to press the bearing out of your old gear and putting it in new one. Ulmer sells gears too, not sure if his comes with bearing.