Nope, only the ATA66 has that ability For you second question, that is unquestionably false. A hard drive's spindle cannot spin faster than its onboard BIOS says to, nonetheless spin faster than the motor actually can spin.
I did the modification to a promise Ultra66 only after I accidentally bought it for a measly $5.43. I would of bought a ultra100, BUT I already bought a raid100 FastTrak before I seen this link! =(
As far as using different drives on a raid, its prefered to use same speed drives, but you could use different sized drives and speed drives with spanning...
I suspect Promise got wise and made them harder to mod.
It's because the cards are so similar (=cheaper to manufacture) that the mod can be performed at all. Promise wanted to save money, but ended up opening the doors to cheap RAID
Well its really thanks to inactiveX, since he spoonfed me the original tomshardware link for the ultra66 tweak.
If you looke don ebay, im sure they have some old promise ultra 66 around.