Bristol and Lund showed what's possible in spectrum below 6 GHz, rather than millimeter wave (below.) That was in May, 2016. In 2017 as I write, production Massive MIMO systems are getting 3x-10 more capacity, a remarkable return for a relatively modest investment. Lund Professor Emil Björnson believes, "20x-40x improvements in spectral efficiency over IMT Advanced are what to expect from Massive MIMO."
Peak speeds in MM shipping systems for 20 MHz typically are > 400 megabits. The universities, working with National Instruments, achieved 145.6 bits/s/Hz on a single 20 MHz radio channel. Today's single channel LTE systems get 2-4 bits/s/Hz, a small fraction of what Massive can do.
Most systems building today use 60-80 MHz (4 bands.) That would allow speeds of well over a gigabit with multi-band Massive. As far as I know, no one has reported field results for more than 20 MHz on Massive. That should come shortly.