Love central vacs. You have have MASSIVELY powerful motors- FAR better than any dyson, roomba, or any portable vacuum. (Look a 'inches of water' along with 'CFM' to judge the power.)
Then vent the vacuum to the outside- this way 'filtering efficiency' really doesnt matter. Heck, just eject all the dirt outside. (not quite of course-the filter protects the motor).
I have a Beam central vac with two outlets in the garage- one between the two doors, for use when detailing outside.
If you are spending $500 on a garage vac, perhaps consider spending the extra $$ and install a central house vac. If you have crawl space or attic, and can DIY it may not be that hard.