I worked 10 years in the aquarium hobby, and I can tell you that a small pump (and that is a small pump) will not be terribly powerful. They will pump to the depth of about 2 feet with no difficulty, but yeah, a really tiny 'aperature' stone will definitely slow it down as you've seen. I used to use 'stones' made of about 20 plastic discs that could be taken apart for cleaning purposes. A bonus was that the discs could be tightened or loosened with a 'thumbscrew' for adjusting the guage of the bubbles
Who knew? When I moved last year, I finally threw away the 20 or so aquarium pumps I had sitting around.
Bear in mind that an AQ pump will suck up whatever air is in the room and push it into your beer, so watch what you're doing in the room. They seem to be especially adept at sucking up cig smoke. An aquarium store may have, or be able to get for you, an inline charcoal and particulate filter (polyester fibers) that will suck out a lot of crapola.