Kruzer,
An .82 should be fine for the ST50. The plane is built pretty light, so you don't need gobs of power, but...if you can fit and balance a 1.00 go for it! Just remember that throttle management thing so bits of Showtime don't flutter off...

I'm puttin' together a Showtime 90 with an Evolution 100+pitts muffler. Plenty of power and noise (I like em that way.)