It seems to me that right now, HP is a bit behind Canon and Epson, who have both come out with newer models since the last Z update. But it wouldn't surprise me in the least if HP comes out with their next-gen printer and leap-frogs the competition before too long. I never liked the idea of paying for the built-in spectro, so have never seriously considered HP. But if you're happy with your 24" Z, I'm sure the 44" wouldn't disappoint.
If you print on both matte- and photo-black you'd probably be happier with Canon or HP over Epson. The x900's are an improvement over past models when it comes to swapping blacks, but it's still more of a hassle/waste than with Canon or HP (where it's a total non-issue).
I just recently bought an ipf6300 and wouldn't hesitate to recommend it or its big brother. As a low-volume printer, I felt the Canon was a better match for me than the Epson. The current pricing on the x300's with rebate is very attractive, especially since you should qualify for the additional "trade-in" rebate because of your Z3200.