I recently purchased a hybrid bicycle (which is a much more road than mountain bike) which I think fits the bill for me. It has no suspension in which extra energy would be wasted, and has an lightweight aluminum frame, seat post and carbon fork, but has straight lower handlebars (I do not feel I can deal with a completely hunched over position for that very long) and has wheels with a bit of tread. The wheels aren't quite as fast as road tires, but provide a little more flexibility. What's more, it shares some of the mechanical parts from the Mountain bike lines.
I think this is about where you are planning on biking and what feels right to you. Try visiting a few local bike stores (stick with bike shops and get away from large retailers) and try biking several road and hybrid bicycles. You may not be able to really get a sense for this cycle with a short bike, however it should present you with a concept of which line to go downwards. Hybrid bikes are less of a perfectly defined category - you could find some hybrids which are quite close to mountain bikes, and some which are close to road bikes. You are probably gonna want to stick closer to the road type.
You will be amazed at how much cycles could cost if you are after high end. For high-end parts you could spend more than $3000 commonly (not including the frame). Certainly, that's highly unnecessary for most people. $1,100 - $1,600 (which is about what I invested as well) can get you high-quality parts and a carbon fork with aluminum frame.
As for the pedals, I've never tried the clipless pedal system, although I know good things.