I fit wherever I feel like fitting, haha. I'm riding a Trek 820, steel frame. The thing weighs a ton. I ride at around 10-12mph on trails unless they're really densely wooded - and up to about 15 on paved surfaces. I could go faster but my muscles just tire out too quickly.

I figure slow and steady will win the race. Besides, the longer my HR is up, the better off I am.