Not quite true. I have the SupraTurbo28 in my A500+ and I simply replaced the 28.xxx MHz crystal in mine with a 36 MHz one already in 1996 or so.
Has worked like charm ever since. No additional cooling (like huge heatsinks or fans) or decoupling tricks required either!
Friend's ST28 went up to 40 MHz, that's because his cache SRAM chips were faster, mine couldn't keep up with that, hence "only" 36 MHz for me.
