nrthwing,

The Yak should fly very well with an OS 160 for aerobatics. I had a 72" QQ Yak with a pumped OS 160 in it. I bought it off a guy who liked to do 3D and it was an awesome combination. I've since sold it to a friend who took the pump off and it does IMAC style aerobatics very well. I'd consider adding a pump to your plane for two reasons. The first is that you would be able to mount the fuel tank on the CG so the flying characteristics wouldn't change as you burn fuel. The other reason is that you will have stronger up lines and you would be able to do loops as large as you want without running low on power. JMHO. Good luck on whichever plane you get. Keep us posted on your flight report.

Fly safe and have fun!!
David