I don't shoot 8x10, not yet anyway. 4x5 is slow but not THAT slow. I can go out with one of my medium format cameras and shoot a roll or so, maybe partial rolls of more than one emulsion with my 645 with interchangeable backs. 12 shots on the Yashicamat or 15 on the Mamiya. In the same time I'd shoot a few sheets of 4x5, maybe two or three photos and a couple of sheets each.
I have trouble shooting 36x of 35mm. I have a roll of Provia in one 35mm body that's been there since July (almost finished though) and a roll of Rollei IR that I loaded in September (2/3s done) and a roll of Neopan 1600 someone on here gave me in exchange for an eventual print from it that's been in the camera for MONTHS. I really need to finish all three up as none are my most used films.
12-15 in medium format is just about perfect. I find my film costs are pretty similar whether I shoot 35mm, 120 or 4x5. I think 8x10 would escalate that a lot, though.