Just another "me too". I run 6.4 code on my lab 3200. It's a non-XM, but with the memory upgrade... so effectively an XM. Being that it is a lab box, it doesn't see a great deal of use, but I left it running 24/7 and never had any issues with it running out of memory or the like.
I'm a big fan of the 3000 series boxes. They don't have the horsepower that the newer ones do, but I get the impression they're a little more stout.