You need the GT version to handle the capacity and even the old set up looked like the dérailleur was getting pushed to it's limits... there are bunch of good choices out there as besides the V Luxe there is always my favourite Vx and Vx GT as well as the Cyclone and Cyclone GT.

I would lean toward the Vx as it is a little more robust than the Cyclone (which is still a solid part).