It also depends on configuration, just changing to a faster accelerator card will effect speed.
2.2mb/s is great for a 30 years old computer.
I got 2.2mb, just by using loads of rom hacks / patches ment for blizzard and A4000.
Normally, I get round 2mb using just my ACA1221 and test 4xbuffered interface. Which is alot better than vanilla stock 1.4mb/s.