Here's my experiences:

Pizazz with ST 51 (stadard muffler), 12.25 x 3.75 fun-fly prop.

I liked this engine on my Laser 3D. But on the Pizazz, not so much. It will hover, but almost near full throttle. Was thinking about putting a lighter muffler on it (i.e Mac's one piece) - this will lighten the plane and give slightly more power... that should do the trick.

But I also have a NIB OS 61SF that I was thinking of trying out.

I wouldn't go for a tooo heavy engine on this plane as you'll need some counterweight in tail. A friend's Pizazz has an OS 70 4-stroke and he has some lead in the tail.

a strong 46 will not hover the Pizazz like you want it to, in my opinion.

keep 'em flying,
scott