b-w,
I think you should look at what you will be doing with the bike in the long run. If you want to do long distance racing or touring, build or buy a touring bike or Randonour bike. But if you think you want to supplement your mountain bike riding with road riding, an entry level road bike would be advised. Road riding is a good way to supplement your mountain bike riding activities for fitness. IF you want to cover the longest distance at the fastest speed a road bike can't be beat for up to five hours or so in the saddle. Assuming you are not carring a lot of gear.