For the most part you're comparing apples with apples. These are both top-of-the-line bows, and are comparable models.
I shoot an LX, and like it very much. Having never shot the Xtec, I can't say which I like better.
When I first shot the LX at the shop, I was taken back by the vibration. Then again, the LX is rated a little hotter than the Xtec (317fps vs. 310fps). Once I got it home, put a stabilizer on it and some limb savers, I no longer notice any vibration. It's a very quiet bow, and I have no intentions of adding string or harness silencers for hunting. I was able to get 310 fps at 70# draw weight shooting a 350 gr. ACC with a 29" draw, and it was still very quiet and very managable.
Like TC said, having the opion of 65% or 80% let-off is nice, particularly if you're into 3D (or if Oregon decides to follow Pope & Young in allowing a higher let-off). I used to be a non-believer in high let-off bows, believing they were too 'snappy' to tune well without giving up some forgiveness. I have a different opinion now...
Whichever you get, you shouldn't be dissappointed. Besides, it's your $50.