I don't see how you could run 2 pumps off 1 varistream. think about it. When you turn the water off on your pole hose the varistream senses the pressure change and switches the pump off. so if you have 2 pumps running it's going to get confused electronically. I know that if I turn the Varistream right up there is a huge ammount of water coming out the brush so A 60PSI pump may well run 2 poles.
I guess it would depend on the working height and most of all the diametre of your pole hose. the bigger the diametre the less restriction on your water flow.
I use 8mm bore for pole hose, still has to go through the jets though. DAI