On my A500+ there is not much difference with an aca500 unless you enable maprom so everything redraws faster and draging screens is smoother. Now adding a blizz030 on it it was same as an A1200 in raw power although it was running on 16bit machine without aga bandwidth. I also have a blizz040/ppc but the best choice for me is the 030 solution. More compatible for daily use than 040 and needs no libs/fixes.
040 on the other hand is faster but whdload meets probs and it is not worth the trouble for just running a few 3D games with 12-15fps than 7-8 on 030.