For me, the mamiya 7 is the fastest non-interchangeable-back loading. Compared to other cameras I've used, the spools pop in and out very easily. If I'm out with the hasselblad and shoot multiple rolls of a couple of film types, I'm not going to carry multiple backs for each film, so eventually I'll have to reload a back, and it may not occur at the most opportune moment... So loading speed is still a factor for me.
The Fujifilm GA645 would be even faster. The rolls pop out almost instantly and once the film is threaded, the autowinder does the rest of the job. VERY fast.