I've heard that you don't want to turn a Ryobi much more than 7000 rpm static
I don't know how true this is but, I do know, my wife loves to run our Weed Eater ( w/Ryobi engine) with about 2"- 3" of line sticking out of the cutting head. That engine has to be turning around 10,000 RPM and let me tell you, she don't care that it has a throttle. She runs it like this until it runs out of gas. Believe it or not, our wackers will last for several years, I haven't had one throw a rod yet.
The issue with the reeds maybe as I read on another web site. The reed system becomes less efficient with the increase in RPM. This would be similar to "valve float" in a 4 cycle engine at a high RPM. So maybe a stiffer reed with stronger impulses to open and close it with increased RPM is the answer to more horse power. HP generally increases with RPM.