Generally speaking, I think the size of the blower has more to do with its portability than anything else. :) Most folks get a larger one for home use, and a smaller one to carry around in the bag or on travel. The air capacity may help with hand fatigue, but the pressure is unlikely to change a whole lot, since human hands really only have so much grip strength. In addition, more is not always better. On the Lensrentals blog, Roger Cicala, in going over their lens cleaning tools, mentions the DataVac, but also that it's too powerful for use on front elements (yes, you can use a RocketBlower for stuff other than sensors).

The Giottos Rocket Blower tends to have a lot of mindshare among photographers for two very simple reasons: 1) It has a valve on the back end, so that air only travels in one direction (from the back to the front) and it never acts like a vacuum, sucking back in the dust you just blew out of the camera. 2) The fins means nothing touches the intake port and you can set it down on the table upright and it won't roll away.