Well, you obviously don't have to take my word for it.

But I have seen guys show up at contests with GMS .25's, and they have always shown themselves to be under powered. And there have been plenty of people who had them who posted their experiences that were consistant. The GMS is about the same as the Magnum .25, which is also under powered. Now, if you know how to work on engines, you might be able to figure out why and fix it, but it's generally easier to buy an engine that produces more power out of the box.

Right now, there is one engine that is clearly more powerful than the others, and that's the Webra. The OS, Irvine, and Norvel are all proven engines with lots of track record.