XT still great, but is it worth the upgrade from SLX or Deore? Probably not.
XT has always been the super nice option without the craziness of XTR. SLX is probably just as good at a lower cost and Deore is now excellent as well. I am not sure the cassette is worth the upgrade. The star of the show for the XT group is the shifter which has XTR style "instant release" faster shifting and double upshift.