First I've never been a fan of any Nexus other than the 8speed ones. They are far more efficient than the other Nexus models and the 8R25 (red label) is the most efficient. Last I read they better internal hubs are now closer to 95-98% efficient. A chain isn't light. Each link can add up pretty quickly when you have an extra 10-20 or so (depends a lot on your biggest chain ring on the back). Keep in mind that this is all rotating mass which requires more energy to move it. You also have additional drag through the little derailleur. Don't forget to add the effects of the chain not being in a straight line.

At first glance it looks like the derailleur should kill the internal hub but it isn't quite as lopsided as you might imagine. I think the vast majority of riders would be very well suited by an internal hub but they are so derailleur centric that they don't think about it. What might be best for a racer might not be best for your normal usage unless you are mostly concerned about speed.

Here is an interesting new Shimano hub, the Alfine, that looks interesting if you haven't already heard about it.

http://cycle.shimano-eu.com/publish/...or_sporty.html

For a good introduction to internal hub efficiency from the perspective of Rohloff see the link at the end. I've owned the Rohloff and still have several 8R25's and I can tell you that in most situations the Nexus feels more efficient and is definitely quiter.

http://www.rohloff.de/en/technical/e...ncy/index.html