The rule for pumping water at height is 1psi=2ft, 1bar=15psi and so on, so if your water pressure into the ro is 50psi then the level of water in the reservoir is 100ft above the ro, so if you want to pump up 60ft you require 30psi, obviously flow rate decreases with height but even the smallest pump will cope with 60ft. As for running 2 poles per pump I would never recommend this to any of my customers as it will halve flow rate per pole and then double it again when one pole is disconnected.