The GT16 & the GT22 are the same width (19.4"), it's just that the GT22 is taller, which allows the extra row of buttons.
GT16: Dimensions: 19.4 (W) x 11.1 (D) x 3.25 (H) inches / 49.3 x 28.2 x 8.3 cm
GT22: Dimensions: 19.4 (W) x 14.1 (D) x 3.25 (H) inches / 49.3 x 35.8 x 8.3 cm
The GT22 is significantly larger than a MFC-101.
I personally went with the GT22, because I like a lot of options laid out in front of me. I'll take a picture of my current board for my Axe-Fx III when I get home later and post it. I'm running two Mission Engineering expression pedals with it, one on each side. All attached to a TrailerTrash 30x18 pro-series board.