I know I misspelled it and I'm too lazy to look up the right spelling.

I am debating whether to replace my Deore LX F/D to an XT or my Deore XT R/D to an XTR.

Eventually I'm going to do both but right now only one.

Would you replace the more often used rear or the desperately in need of upgrade front?

I wouldn't replace either one but if I had to choice, the most used and the one that is the most complicated, the rear. The front derailleur is very simple, I'd let it go.

I guess then that begs the question of why wouldn't you replace it?

I would not replace either derailleur, either. There is not significant performance difference between them. At this level the shifter has much more effect than the mechs.

Wait until the derailleurs wear out or break (which the front will never do) before replacing. Then get the model that is best value.

I have already upgraded to XTR shifters, have a high end tubeless wheelset, carbon everything, King headset... not sure where else to go outside of crank, fd, rd, and saddle. I alrady have the XTR brakes on order so that's done too.

If it begs the question, why are you asking?

Upgrading just makes the bike and your wallet lighter. At this point the weight difference is small.

I'm aware that it's small. I'm sort of a weight weenie with my mtb, and you can't tell me the XTR stuff doesn't perform much better than anything else Shimano makes for mtbs.

XTR shifters are bad ass for sure, but don't neglect the shift cables and housing either. They can make all the difference in the world when it comes to drivetrain performance.

Actually, I can. When used with the same shifter, cassette, chain and cables, the performance difference between an XT and XTR derailleur is not detectable.

ViceLord, I support your purchase of the XTR and XT derailers. Please continue to support the economy.

If you have that much money to blow, there are a few other upgrades that are actually useful. What fork are you currently using? What wheels? What kind of frame is it? And geez, if you still have that much money burning a whole in your pocket, I could use a Fox 831 and an F120. And a set or two of I9s.

Lol! Scandium kona frame, fox vanilla r fork, easton tubeless wheelset, yup. Cassette and chain are garbage i didnt think of those.

From someone who wasted money going from a Hone crank to an XTR because it was half a pound less and I was stupid, you notice absolutely no difference swapping the crank (in my defense, I bought the XTR cheap at Veloswap). The only good part is I was able to put the crank and middle ring from the Hone on my DJ.

I hear ya, but the crank is part of a 10-speed conversion that will eventually happen, that is when I get all the parts together.

Then you have even less reason to change the derailleurs now. 9-sp derailleurs are not compatible with 10-sp shifters. You will need to change the rear derailleur, shifter, cassette, and chain all at once. You may be able to keep the crank and rings.

You're worried about derailleur weights and you're running a coil fork?

it's all in steps man, all in steps. I am getting the cheaper stuff done first.

Not cheap to buy new 9-speed parts if you are going to switch (notice I did not say upgrade) to 10-speed any time soon.

Don't replace either if you don't need to. I was told (on this forum) that the difference in performance between XT and XTR rear derailleurs isn't nearly as large as the difference in price. And replacing a front derailleur when your current one isn't broken seems completely pointless. Save your money and replace the forks or rear shock (if you have it). They usually wear much sooner than the derailleurs.