Theres a good reason why the Mac Pro has six Thunderbolt 2 ports: current Thunderbolt tech isnt powerful enough to drive more than one 4K display per port. Future computers shouldnt face that limitation, though. VR-Zone has leaked a presentation which suggests that Intels next Thunderbolt controller chip, Alpine Ridge, has enough bandwidth (40Gbps) to drive two 4K screens at the same time.