What precisely is different? Every time this sort of thread comes up some nut-hugger swears there's so much difference between one brand and the next, I have yet to see any real evidence.
This is because of some magical DC pixie dust that makes the same circuit perform differently, or possibly just the way each derives their specs? Also if you think you're going to see anything near those published efficiency specs real-world you're out of your mind.
You will never get a legit answer to this question because there will be no statistically significant difference in performance.
So what precisely is different besides the heatsink?
Actually none of them make amps whatsoever. Mmats makes amps, Zenon makes amps, Zapco makes amps. The companies you listed buy amps from Korea to slap their brand name on. There's a very few designs and 2 or 3 build houses. IMO the only thing that should sway you from one "brand" to another that would justify price is customer service and how much value you put on that. That's not dowing any of them, and I'd certainly not discourage anyone from running any of those products, but let's call a spade a spade.
I've clamped more than that out of mine when I ran one (that was a fantastic little amp), but that's a whole different animal. PAI series amps were same as Atomic/Sundown amps of that time period.