Noah sent me this link, which is about a study comparing various combinations of road vs tt setups. Since I just bought a tt bike, I find it exciting to see the power savings that they measured between the two! I don't have an aero helmet, but comparing the drops on the road bike to areobars on the tt bike, I hope I can bike up the pace a little next season. ;-)
Key points, taken from the website:
Position: Going from drops to aerobars will save you ~30 watts at 40km/h
Bike: A time trial bike will save you ~20 watts over a road bike with clip-ons at 40km/h
Helmet: A time trial helmet will save you ~10 watts over a road helmet at 40km/h
