Need advice on which hardtail to buy!

I posted this elsewhere, but thought it more appropriate for here. I'm looking to pick up a new hartail, and there are three bikes with the same frame but different components. They are as follows:

Full XTR carbon crank ( Sid race) (discs): 19.1lbs @ +300$
XTR/ XT(discs)(sid race): [email protected]$
XT/LX (no discs)(sid race) 21.5lbs @-300 (-600)$




My question is this: Yeah, it would be nice to have full XTR and a carbon crank. Hell, you're riding a 19lb hardtail. However, I was originally going to get the 21lber xt xtr, because it's a step up in components from my stumpjumper. However, for 300 less I can have a 21.5 lb hardtail anyway. Sure, it's only going to be xt lx components, but it still has a sid race and is only slightly ( in my opinion) heavier than the more expensive bikes. I want to be to keep this bike for at least 5 years with potential to race it at all levels. So, my question is this, ulitmately:

Full XTR carbon crank (discs): 19.1lbs @ +300
XTR/ XT(discs): [email protected]
XT/LX (no discs) 21.5lbs @-300 (-600)

I'm a firm believer that its the rider and not the bike, to a certain extent. So, let's say my fitness level is high enough to race with guys who all have very light bikes. If I do get the xt/lx which will likely come in at over just 22lbs with pedals, will I be at a disadvantage? I could afford the full xtr bike, but I feel as if it isn't too necessary. Does XTR really offer suprior performance, or is it simply weight? Likewise, is XT that much better than lx? I'm only saying this because if I get the least expensive bike, I can also afford a 29er. On the other hand, i don't want to sacrifice performance, because I plan on racing seriously in the future. thanks for your time. i appreciate it.
Thanks!