RE: Magnum Engine Question
The Rossi 40 will work ok, but its going to result in a nose-heavy airplane.
The MVVS would be ok. Make sure it is bench run first and runs well.
From your list, I'd personally go with the Irvine .40, and put a tuned muffler or pipe on it somewhere down the road.
Hard to estimate speed based on engine. But figure if you can get a 9x7 to turn up around 16K rpm on the ground, you will get something in the 100-120 mph range.