Ben one thing I have noticed and this is not intended as a knock but purely an observation. Your company seems to change machines and units alot.
You do know there is no silver bullet, don't you?
Machines are only as good as the technicians using them. Big "may" clean better IF the technican cares enough to put out the effort, otherwise it just eats up more fuel hauling it around.
A "good technican" with an average sized unit can out clean an "average technician" with a big unit.
(we are still talking about tm's....are'nt we?

I was anyway.)
I'd tend to side with Crowley, it doesn't always have to be big......umm TM wise.