Which makes more sense to me, too. 
The hint was having the error Go Away™ at a slower speed, which reduces the overscan distance at a constant acceleration.
You want to crank in as much acceleration as the hardware can withstand, without having it shake too much when it settles down at the next position. Ditto for the maximum speed, which should be as high as possible without losing steps due to the lower torque at higher speeds.
I have yet to convince myself the factory settings make any sense on my OMTech 60 W red/black, so your homebrew values may not be very wrong at all.