Thats some interesting information and helpful to those of us considering a new printer. I do have a question for you and others who have used the HP Z series and especially if you have had comparative experience with Epsons. Metermarism issues is this a noticeable problem with the HPs, either b&w mode or color?
I take it you're talking about colour constancy and grey balance failure. Otherwise do you mean illuminant metamerism between Epson and HP?
If it is colour constancy, the HP holds it's own with some quirks. The Gloss Enhancer has it's own bronzing but is not very distracting. The bronzing is not going to add any coloration in changing light sources.
Between Epson K3 and HP Vivera the illuminant metamerism goes in opposite directions. I find the Epson goes towards red magenta, whereas HP goes green cyan blue as the K temperature goes up if there is uv. At low temperatures both are fairly consistent , HP having a better look at say 2800 K . If you make profiles for these K values both adapt very well, and both are easily corrected.
Overall greyscale repro is harder to put into few words. Gloss Enhancer is an essential element for reducing shifts in constancy, so comparative tests have to be done with it on. On matte paper however where matte K is used the HP inks are more neutral than K3.
There is simply no one who can put a label on which is better or worse, simply different.