This may seem like a dumb question, but wouldn't "gearing down" a shop vac by using 3-6" tubing onaccomplish the same as a dust collector.
I'm somewhat familiar with the same ideas if you want to move water. There are high flow, low pressure water pumps, then there are low flow, high pressure pumps.
Or perhaps the answer comes back to HP. I recall someone posting on here that shop vacs come nowhere near their advertised Hp, but that dust collectors take the high road by giving you an honest HP rating.