I do not have experience with dual rotovac of same butler....I do a lot of dual van on the same job site just because of some of what your are describing.
But, I think 2 360i units would actually work because your flow rate would be ok (as I run 12 flow wands and Zippers on each Butler alone)
And with the Rotovac's (360i) you would probably have that same water flow rate with the 2 units, and you would have suction contact on the carpets all the time....so yeah, that has good potential...
I find what you are talking having your tech working at the same time with you, really helps get them more comfortable in the field and also the homeowners more comfortable with them alone next time cleaning.
I actually have found that even if it worked for you sometime, running 2 vans on the same job sites (with good planning) has been saving and making us more money...and putting less miles on the vans...and just a slight increase in Truckmount hours.
I am doing a presentation on this again next week in Atlanta, and each year I run numbers, I am more surprised at how much better we are getting in efficiency with this....
But also, before I forget, I would definitely recommend the high heat for your situation...and honestly....I really love that high heat option.
You have peaked my curiosity now, and might have to try and locate two 360i units to try this...I have 360 XL units (2 of them) and might try it just to know with those units.