Hey guys, I was just flying my Vector 300 extra today here in northern Alberta, Canada.
Temperature was around 5 degrees celius.
I have a OS 91FX on it with about two gallons of fuel through it now.
The bad news, not unlimited vertical.
Pretty good vertical, but, not unlimited.
I put in a 16 oz tank and when it is full the plane will porpoise somewhat, you have to watch the elevator.
This plane is about the toughest one I have ever owned, hands down.
Very good build quality as well, they say the 540 is the same.
I don't know where the weight of the 540 compares to the 300 but the OS will not provide unlimited.
I would think a 120 two stroke would be perfect.
Hope this helps.
Lean540