Ahh Positive rate, I think you're confused there.
We're talking Transition levels and they don't vary from aircraft to aircraft at all; sheesh, imagine the accident rate if that were the case.
They vary from country to country, eg 18000 feet in the US, 6000 feet in the UK, 11000 feet here in New Zealand and so on.
AmericanF100, to answer you question, generally "Knots" are used below transition level and "Mach" (a percentage of the speed of sound) is used above transition level.
Also, altitude readings above transition are known as "Flight Levels".
An aircraft climbing through transition level will have to reset it's barometric pressure to the standard setting of 1013.2 millibars (29.92 inches of Mercury).