I have seen this plane flown with both engines.
The Saito 180 will fly the plane with authority but will require a pound or more of lead in the nose to balance it. As previously stated the 180 is also VERY thirsty. The Zenoah G26 will balance the plane with no additional ballast but only gives very scale like performance. The G26 is very economical to run as stated previously.
If you are looking for power the Saito 180 will get you there, but at the price of expensive fuel.
If you are wanting a very scale flying plane the G26 is the ticket and cheap operating, but the down side is lack of performance.
Just depends on how you want to fly it.
I can't comment on how climate affects the engines. It doesn't get that cold here (compared to you).

wcb

You didn't ask about other gas engines so I won't go there.