PTO High Idle will lock the torque converter and spin the engine at 1200 RPM (adjustable with rheostat if you want). Battery Charge Protect starts off at 1200 RPM and ramps up if there's a low voltage situation, either to low batteries or if you are boosting something. I have both wired up, but can't ever remember the wire colors.
I run the PTO to warm up the truck in cold weather. I use the BCP allot when boosting, etc. It really ramps up to match the load. I have a voltmeter mounted on my pillar so I can really see what's going on. I've boosted plenty of other pickups, tractors, trucks, irrigation motors, you name it, it really puts the power to it. It will spin over 2000 RPM if needed, I believe it goes up to 2400, but never seen it that high.