ACA500 is a 14MHz card. If you add fastmem on the 86-pin port, it's going to be slow (7MHz). Also, as I wrote numerous times before, I don't support anything that may be connected to the 86-pin or other ports of the A500. The card is extremely low-cost and can only be that cheap if it works out of the box. As soon as the customer adds other stuff, it's either fully supported by iComp and resellers, or you're on your own. Since the "on your own" part pretty much always ends up on my desk, I make it mechanically impossible to make mistakes.
Here's some info on how fast the ACA1220 (16.67 MHz) will be:
Overclocking is possible but not recommended and not guaranteed:
I have also attached the AIBB modules to this message.