First Driver thoughts:
I now have HP drivers installed on Windows and Mac. Windows had 3 choices, I went with PCL 6 v3. It's going to take time to sort through them. I also have reference prints from ye olde inkguzzler on Photo paper.
With these choices, first of note is that the Windows and Mac drivers yield very different results. Is it different color matching? The Mac output has more contrast by default. Printing on Mac more closely matches the inkjet and monitor reference (which are actually pretty close to each other). Enhanced produces more colors than Normal, though perhaps overdoing the saturation in the process. Inkjet on Photo paper does show less texture and a larger gamut (ofc) but the Mac Enhanced prints are pretty close. The Windows prints were farther from the reference.
Their were only minor screening differences between Standard, Enhanced, and Fine Lines on Windows. Both Win and Mac with the M776 handily beat the inkjet on plain paper.
I also need some better laser paper! So much to try...
Yes, the paper makes a DRASTIC change. It is impressive, to me at least, that even with crap paper, if you use 'enhanced' (on mac) it does a really better than expected job. You get magazine slick results. But it does improve greatly with good gloss paper. I have a link here where I found some stuff that works well for me. YMMV.
Also, the color matching is pretty great out of the box for me on the Mac. I havent tried windows, but I suspect that is a difference.