I agree with what tbone57 said except there is a third option you could consider, too: take US 285 from Denver over Kenosha Pass to Fairplay, then go south and pick up US 50 at Salida. Here are a couple pages that you might want to look at:
Motorcycle Colorado Great Motorcycle Roads Near Gunnison - Motorcycle Colorado
Be sure to bring warm clothes. It gets cold at high altitude even in the summer.