i only get about 12-18fps.
320*200-16b.. and aga mode in ham8 is a bit
faster.
That's because 320*200 16bit requires 128000 bytes bandwidth whereas 320x200 HAM8 requires only half of that (64000). Mediator bus is only slightly faster than chipram bandwidth, especially on phase5/dce hardware. Broken hardware (wrong bus timing) such as Apollo accelerators give faster mediator bus access.
Yes, in simple terms, AGA is faster.