ORIGINAL: Tired Old Man
You would most certainly notice the loading difference between the ZDZ and Zenoah. I few this particular plane in a few different variations and in each case the lighter one flew better than the heavier one. When the Sig Sukhoi was designed there was not as much attention paid to airfoils as there is now so the wing planform is not as good as it could have been. It actually flys best with a lightest engine that has the power to fly it.
Well of course, lighter is always going to fly better. In a perfect world, he'd be using a Moki 2.10.
But he asked for opinions......... should he use the motor he's got or spend $600 on a new one? I personally wouldn't even fly it. Too small. I'd sell the engine and the airframe and put the cash into something larger. But if he doesn't want to sell the stuff right now, then mate 'em up and fly it until the cash situation improves. Not every plane in the world is a 3D monster. I think it will fly just fine for sport aerobatics. Even entry level IMAC.
Just my opinion. Not saying anyone else is wrong. I really think people worry too much about wing loading. It is what it is.