I would start my shopping with looking at the print heads first. The machine is just a machine to move the print heads back and forth. Some have better features than others, some cost more than others. But the reality is about the support, and the print heads. Right now there are many of print heads that can handle the kinds of speed you are requiring, but not a photo quality. Not even close. However, there are a couple that can. Konica Minolta 1024 print heads can handle the speed and drop a an ink droplet as small as 6pl. Plus the print heads are 72mm wide and usually manufacturers stagger their layout and can leave an impressively wide swath of ink in one pass. I've been reading good things about Ricoh Gen 5 print heads, which also lay down a small 7pl drop. But I don't know anything about longevity with those. But they've been in the game well over 30 years making print heads. I think the real difference between the two would ultimately be the RIP and the drivers. So I'd be asking to see lots of print samples, and verifying at what speed the samples were printed at.
The other thing of note when shopping for a flat bed printer with white ink support is how it handles the white ink separately. Meaning, does it recirculate the white ink continuously even when not in use to keep sediments from building up, and the titanium oxide from clumping and clogging.
And when printing on acrylic... always ask about pre-treatment, and if it's a necessary step with getting the ink to stick. I have pulled off images, like a fruit roll-up from acrylic that wasn't pre-treated. As their ink formulation wasn't geared for low energy surfaces to begin with. But that's just ink. Many manufacturers of ink out there, and you can get whatever you need, provided to you know what to ask for and who to ask.
