Looking to get a saw to limb with

We see the same thing in many other engines and applications. It's actually called Torque Rise. Pull an engine down below it's torque peak and it falls flat on it's face. The more area under the curves, the better. But you can alter engine parameters to optimize torque characteristics for the application. There was some discussion years back (with a major mower OEM) about why diesel engines weren't more prevalent on commercial lawn mowers despite the fuel efficiency and reliability advantage and yet dominant on tractors. With mowers, most diesels were losing more RPM before the torque rise would stabilize the load. So in thick, heavy or wet grass, you lost more blade speed than what was desirable where a gas engine's torque peak was much higher up the RPM band, so while it didn't make as much torque as the diesels, it threw it's heart into the battle quicker.