I don't know the full set of differentiators.

For me (not quite at the A1000 level, but just above -- still in the prosumer price range), a major one is ECC.

Thermals and size are a bit better too, but I don't see that as $500 better. I actually don't see (m)any meaningful reasons to step up to an Ax000 series if you don't need ECC, but I'd love to hear otherwise.