OK, quick question - what's better (if any) between the A2000 and A4000 HC8+ cards, or is it just the difference in chipset?
Just a different chipset, as far as I can tell. GVP had a terrible, terrible habit of releasing the exact same product (or nearly the same product) under at least a half-dozen different model names. :p
My .02 cents, go with any of the GVP models and max out the ram (8MB of 30-pin simms can be found for under $15), get the latest 4.15 ROM from TJLazer (also around $15), and done. If you feel like inflicting pain on yourself try to find a GuruROM, but with the pricey little adapter... good luck!

As an alternative the old "tried & true" A2091 isn't a bad card, and you can upgrade the ROM's and WD chip and do various performance hacks on it, as well, but it's limited to 2MB of memory expansion.