Originally Posted by djSlvt
I've contacted Sheldon Brown for advice. Asking him for replacements for my 105. He told me that 105 is nothing special, and his personal choice would be XT.
Thus, his personal choice would be mountain bike der for your road bike. Why?
Is XT better than 105, Ultegra, Dura Ace? I got the sense off him that it is stronger and shifts faster, but isn't lighter, but who cares. What are you thoughts on this one?
"Mountain bike" and "road bike" are
marketing terms, not technical terms when you're talking about derailers and many other parts. The XT is what I would call a "wide range" derailer, vs. medium range (105 GS) or narrow range (105 SS). Wide range derailers were also formerly called "touring" models, but in the late '80s, the marketeers decided that "touring" was a worn-out term, so they re-named all of the touring stuff "mountain." It's a mistake to get suckered into thinking that there's some incompatibility where none exists.
The XT would permit a later change to a wide range cassette, while the so-called "road" models generally won't handle anything bigger than a 30 in back.
In terms of "level" (again, mainly a marketing issue) XT is the same "level" as Ultegra. Indeed, I replaced the Ultegra that came on my Raleigh Cadent 4.0 with an XT. I actually didn't change the gearing, so the XT is working at a small fraction of its capacity with the 12-25 10 speed and triple front.
I switched to the XT partly so that I would have the option of going lower in back at a later date, but mainly because it is the low-normal "RapidRise" version which provides slightly better downshifting. The use of a low-normal in back also reduced confusion when I would go back and forth between my Campagnolo equipped bikes and the Raleigh.
Sheldon "Reality, Not Marketing" Brown