Binary_01,
First of all, flying a Sig Wonder slowly is almost an oxymoron. They are designed to fly FAST. If you read the Sig Literature it says "If you blink your eye you'll Wonder where it went", that's why they gave it that name.

Second,
A .25 is really too big for it. I thought about putting a 25 on one, but after reading the instructions, looking at the kit, and talking to a few people I came to the conclusion that a 15, maybe 20 max, would be a better motor. A 25 FX weighs too much and will pull the plane apart.

Third,
This plane is a handful. First off, you have to hand launch it which can really take some quick reflexes to manage. Since you're posting this question in the beginners section I assume you are still pretty close to being one. This plane needs some experience under your belt before you fly it. I'm not trying to talk you out of it, because it is an absolute blast to fly, but get some more experience before you fly this.

That's my 02¢ worth