The more upright you get, the more aerodynamics works against you. However, I think the whole concept is sometimes overplayed with many cyclists riding bikes with ridiculous handlebars drops that are clearly uncomfortable. I've got all of my bikes set up with the handlebars the same height as the saddle. I am more upright than most when riding on the tops and hoods, but can comfortably ride in the drops for as long as I want (something most cyclists with huge drops cannot do).

Anyway, check out the new Salsa Casseroll if you are looking for a faster bike that allows a more upright position. The Casseroll has a very tall head tube, making it very easy to raise your handlebars higher. I can easily average 18-20 mph in group rides on the Salsa, so the taller head tube isn't holding me back.