I can't remember the exact figure, but I though the later Minis on 12" wheels with teh 3.1 diff did about 20mph per 1000rpm?
Only, either the thing I have got is very quick (for a 998cc!), or the speedo's very optimistic, I'm trying to work out which!
It's an 87 Mayfair, so should have the longer diff, and seems to going by the red line in lower gears (31mph in first)...
Anyone got a reference for speed per 1000rpm in each gear kicking about?