Along the lines of your other post, I already OP & have thought about what you're talking about. A 175 w/ a tank will do as good a job IMO.
With OP, sprayers go out like a banshee due to the chems used. At least they have for me. I'm part time & have been thru prolly 30 sprayers in 5 years. The first few I didn't realize the OP juice was clogging em up. After that I started to clean em. Didn't matter. Maybe I didnt clean em long enough. Still, if 10-15 minutes cleaning-running water thru- 1 piece of equipment after every job isn't enough, what good is it? Sprayers & OP chems were not meant to be together.
On one job not only did my main sprayer go belly up, the back up went out too. So I put the solution directly on the pad. That looked just as good, if not better, than the parts where I presprayed, let it dwell, then padded it.
So that led me to thinking a 175 w/ a gravity fed tank could be the way to go. Ya put down the juice & scrub it in w/ a carpet brush. This would work in the pre-spray real good. Then go back over it w/ the pad using the same machine.
A friend from another board said he went to a 175 from an OP machine & it works just as well. That's w/out using a brush to scrub in the prespray.
I don't know for sure how my idea will work out, but it seems like it's worth a try. I'm starting to wonder if the effectiveness of OP isn't based more on the juice & pads rather than the "OP" action. I'd think a 175 w/ the same juice & pads as an OP machine could do the same quality job.