Yeah, if you price out the difference between the Experts full XT components and the Comp SLX-XT mix there may be about $150 there and maybe 6oz of so of weight. With the XT shifter you get the two gears at a time upshift as well as downshift. The 600 series is gonna be better brakes, but not much difference in price. And then you have the adjustable stem.
I think the XT cassette is aluminum where the SLX is steel alloy, so the XT is lighter but perhaps not as durable.
So about $200 in price difference can be explained by component upgrades.
I decided on the Comp because that was pressing my level of price comfort. I went in looking at the sport disc, but decided I wanted shimano brakes and dual crankset... which put me into the Elite, and then the lighter weight frame... well you get the picture.
Had it to do over again, with what I know now, I probably would have sprung for the Expert, but I think they were sold out at the time anyway.
I guess, if you can find a LBS that stocks both in your size, ride them both and make your own judgement.
Oh you can always add the XT shifters to the comp later, I think there is the biggest difference between the models real world.