Hi Mike,
In my opinion, Jim Martin nailed it. A good operator can get the carpets clean using a TM or a porty. A TM is faster but at a cost. A porty is some what slower, thus a cost. Many guys started out with a porty, little or no debt and built their business and can now afford a TM. (some are very expensive, but the guys who buy them feel it's a good investment, and reading their comments we can see their point of view)
I've often have ask myself the question when is enough, enough. How much power do you need to clean a carpet. The longer the hose run, multiple wands, the more power is needed.
To try and answer your question about cfm and suction (water lift) here's my thoughts. Use a water pump for example. Pressure like water lift is important, but if you have an extreme psi and no flow (cfm) you wont clean anything. Now if your pump has no pressure but only flow your cleaning is also limited. So it is better to have a balance of both than extreme on one end and a deficiency on the other. That being said, the more lift and the more CFM you can get in balance the better. Portys are limited for obvious reasons. There's only so much power in a wall plug, but they still can clean carpets. I hope this helps.
John
