Actually Gordon and Molar Mender are both right.

The first set of turbine rules adopted by the AMA in 1997 or 1998 limited the thrust to weight ratio to between .5-1 and .9-1.
(The interceptor I was flying at the time weighed about 20lbs at takeoff, and was flying on a 8-1/2 lb thrust FD3-67)
I don't think there was a speed limit.

The speed limit was introduced in the next drafting of the rules as an appeasement for loosening the thrust to weight restrictions.