I only run three bits of XTR kit on my bikes, rest is all SLX on one bike and all XT on the other. They are:-
1. Shifters. XTR have four sets of ball races versus the XT two (and SLX/Deore nylon bushings!) and it does make them smoother. Plus good deals around on 10sp XTR shifters at the mo (Merlin XTR same price as CRC XT) cos they’re sooo last year now the 11sp is out!
2. Chain. But that’s because I live near the coast and any exposed bit of steel that’s not coated in something to protect it will rust. XTR has nickel plated inner plates, outer plates, and pins. XT only the outer plates are coated, SLX neither. The fact that XTR has hollow pins is actually a negative for me as they get full of gunk and are impossible to clean out, but the fact they don’t rust wins the day.
3. Bottom Bracket. XTR are supposedly better sealed. Haven’t done an exhaustive scientific test to prove it one way or ‘tother, but as they’re cheap as chips bought online from Germany – just makes sense.
You’ll notice none of it has anything to do with weight, and two out of the three you can’t even see an XTR logo – so its about function not weight/bling for me.