3-5 hours of riding technical trails with climbing sounds like a prescription for Iron Mtn. Casey is the expert in that area. My suggested route would start in Damascus, up the Creeper Trail to Beech, hit Iron Mtn to Rush, down Rush, back up FR90 or Sawmill/Feathercamp to Iron Mtn, back toward Beech but stay on Iron and head down Mock Holler into Damascus. The National Geographic "Mount Rogers" map covers the area well.
Bike rentals are available in Damascus but all I've seen are entry level bikes. If your riding the 27th there is a chance I could show you around if you don't mind waiting. Limited riding in 2008 has really hurt me.