I need to build up new wheels for my Mpire-right now it has rhynolites and a doublewide-and im not liking either of the rims. I want something on the lighter side. The front hub is 36 spoke, the rear is 32. The rear is 165 spacing so its a strong wheel. I was looking at 521's, or if i can find them 321's(cause the 321's are cheaper then the 729). What do you think? what about singletracks? or a Sun Rims equivalent to a 321.