I've got the VXL-30 at 33mhz(I think) with 2mb ram installed in my A500.
The machine is very fast, responsive, etc. I remember doing benchmarks back when I first got it, and I was impressed. General operations, like compressing/uncompressing was much much quicker.
I'm in the process of upgrading from 2mb -> 8mb. Hunting down the chips has been a PITA but I think I finally found some compatible chips, and in combination with an adapter (which I'm not sure if I can get yet) should do the trick.
Keith