ORIGINAL: gaRCfield
All I know is I tried very hard and talked to a lot of respectable pilots in different flying categories (pattern, IMAC, and 3D) and found that it is very difficult to find a happy combination of 25% plane and gas engine. 26cc is not enough power (for aerobatics) and 40 cc is too much weight. What is the wing loading on the Yak with the 40cc? What happens when it dead sticks? I thought about getting something very similar, and these were the questions I was asked. And of course there are always exceptions, and you can get things to work that are not optimum.
The Yak has a 50cc and I've never seen it dead stick since it runs well. I can only assume the wing loading is good since it handles 3D flying very nicely.
My point though was that you have to be careful about just throwing out advice with limited experience. I even shy away from answering some questions on here since I've only been at this 5 years or so and I'll be the first to admit I've put my foot in my mouth on here on an occasion or two.
The advice you got may be right on for the type of plane and flying you intended to do but it is not accurate in every case. There are a vast multitude of aircraft designs and engines out there. You can't just say a gas engine won't work on a 25% airplane. What kind of airplane is it? How much does it weigh? What gas engine will be used? How will it be flown? Sometimes the gas engine will be optimum.
I'm not trying to be a jerk, just trying to get you to see that there is often more to the story.
25% airplanes generally don't fit into a beginners forum though so I'll shut up about them.