Looks like a 28MHz overclocked 040/25MHz) model . I still have my 35MHz Mercury. Ran like a top for many years 24/7 running my BBS. Not sure about the SCSI problems. Once I switched to 3.0/3.1 it was more stable using the "do not use" jumper. (Might have just been a placebo, but someone on usenet tipped me off to it...)
Edit: I guess the seller does say the speed. Getting it faster only requires an oscillator, faster RAM, and maybe a faster 040. Mine was bought without CPU and I have a 040/40MHz in there underclocked.
