I just discovered a handy online-tool for comparing the size of various cameras. Here’s a few comparisons I ran that are very telling of the size differences:
Nikon D810 w. 14-24mm f/2.8 Pro vs. Oly E-M5ii w. 7-14mm (14-28mm) f/2.8 pro:
Nikon D810 w. 24-70mm f/2.8 Pro vs. Oly E-M5ii w. 12-40mm (24-80mm) f/2.8 pro:
Nikon D810 w. 70-200mm f/2.8 Pro vs. Oly E-M5ii w. 35-100mm (70-200mm) f/2.8 pro:
Nikon D810 w. 24mm f/1.4, Fuji X-T1 w. 16mm (24mm) f/1.4, Oly E-M5ii w. 12mm (24mm) f/2.0:
Nikon D810 w. 85mm f/1.8, Fuji X-T1 w. 56mm (85mm) f/1.2, Oly E-M5ii w. 45mm (90mm) f/1.8: Interesting thing to note, the Fuji 56mm f/1.2 will provide the exact same field of view and depth-of-field as the Nikon 85mm f/1.8.