There is a great write up on the Toyota Supra at wikipedia.org:
Toyota Supra - Wikipedia, the free encyclopedia
It is provides a great history and some technical detail. It mentions the 7M-GTE MA71's (turbo) have a top speed of 156mph, but that is the only reference I saw related to speed. Not sure about non-turbo.
Maybe someone has some real life experience above 100mph which is about as high as I cared to push my 88 stock N/A .