What's the course like? A flat, windy course is good for a rear disk, a hilly course is good for a lightweight wheel. There's a point at which they don't matter much, maybe low 20's average speed, especially if you aren't a flyweight where every ounce makes a big difference in the hills.<br><br>
For that kind of money, you might want to consider fresh tires and a tighter rear cluster to use for the flat courses, those two things can make a nice difference for about 140 bucks and you never have to return them.