Regardless, they are still a belt and pulley systems.
They CVT and the HST are worlds apart as far as the reliability factor.
Not to mention the other benefits that the HST system provides.
Unless you are operating a PTO driven implement. In which case you will need to run it at the required rated RPM. This is usually indicated on the tachometer with a distinct line.
Turbos, injection pump mods will not increase the speed of your RTV. Well, if you increase your high idle by messing with your pump you may get a couple more MPH as mentioned above.
The only way you could get more speed is to mess with the valving/swash plate in the transmission. I don't don't...