Might be different for some, but for me speed knee is that extra push you give during the down push of each knee.
The known open voltage is a good reference for deciding which controller to get so it can handle spikes , say if you disconnect the loads on purpose or by accident, but its more important to know the max voltage and current you'll be getting from the pedgen and using to recharge the batteries.
PLUS you'll want one that hold the max voltage to the type of batteries you are using.
Bruce S