He does repairs on all brands but he doesn't stock any of the GMC models.
One thing though, he told me that the 25cc homelite on the bench produces around the same RPM as the current model ryobi
31cc. But the ryobi has more room for improvement and he has tweaked a few and got around 9500 rpm mainly buy changing the muffler and carb. I asked him if it was safe to run a ryobi at that rpm and he said the one he tweaked is his own that he uses at home and is still running strong. He said the main issue with running at this rpm for extended time is heat build up which could cause damage to the bore. His is used as intended (As a Brush cutter) but don't know what sort of results we would get with an 18x8 prop. He said it's best kept at around 7500rpm according to manufacturer recommendations.