My experience is quite narrow and limited to my XT-equipped Nishiki Alien and the opinions of the guys at my LBS whenever I needed to replace parts 15 to 20 years ago, and I was given the impression that the XT stuff is a little bit heavier, but a lot stronger and thus longer-lasting. I'm sure it depends on exactly which components, though. Has anyone actually made and recorded any weight comparisons?
Not a complete list, but weight generally seems to get less as you move from Deore -> XT -> XTR: http://weightweenies.starbike.com/listi ... erailleurs
. Interestingly, things don't seem to get any lighter as we move from 1990s to 2007/8, some models seem to be gaining weight.