Don't call it XX - it's Double-X, DXN, or 5222.
It can be best described as the missing link between PX and TX, but it's the same emulsion as it was in the '50s. PX and TX on the other hand have been updated a few times since then, so DXN is the closest you'll come to that "old Tri-X" look we know and love from '60s press photograhpy.
It is correct to note though that its designed to be contact-printed to dupe films rather than directly enlarged. Be interesting to check whether or not a diffusion or condensing enlarger makes a difference though...
For those of you attempting to buy via Kodak on-line, you should note that that's a very new endeavour for them and they may not have ironed out all the creases yet. For a long time you ordered by fax or phone, so that's probably the way to go if you're impatient. Note also that the shortest distance you'll get is 400 ft in one can as one roll - you'll need to break it down or load directly from the full roll.
The two ORWO films are both very good and are also old-style emulsions, in this case derived from the very early Agfapan films and fifty years of East German experimentation :P I've no personal experience with them but I like what I'm seeing on Flickr.
A good film to check also is Kodak HAWKEYE Surveillance Film 2485. Comes in 150 ft rolls on ESTAR Thin-Base and is nominally EI 400. Stunning latitude though, and extended-red sensitivity as well. Trade-off is high grain, but again it looks okay and also prints quite well. I got a bunch for AU$21 per 150 ft but that was second-hand, so I don't know what list price should be. Comes from Kodak Aerial and Industrial instead of the professional imaging departments.
Failing that, can't go wrong with bog-standard T-MAX, and the price is more than reasonable considering what you're getting.