Hi Rob
This is a gut feeling from experience rather than knowledge of the technicalities of the issue.
As can be seen from the basic versions of Amtek's 3 stage vacs, there are 2 options. The 5.7" high rpm speed or the lower rpm 7.2" If the 7.2" were made higher rpm to give a greater performance, it would disintegrate from centiftugal forces. In the early days of series mounted vacs, reliability was an issue so the use of the 5.7" became the norm.
IMO, to develop these types of vacuum motors to develop more performance, although feasible, would not be cost effective.
The only other option for a portable would be to go the Bane-Clene route and have a small blower. But the weight and cost is normally prohibitive. The Bane, although a truck based electric, does have the facility to remove and take indoors. This would only be viable inthe likes of The Empire State Building.
Safe and happy cleaning
Ken