The problem with using a centrifugal blower in a driven (rather than turbo application) is that the boost is proportional to speed, this means that the low speed boost is poor when compared with a conventional supercharger.
You are right in that the efficiency of a centrifugal blower when on boost is significantly better than any rotating lobed supercharger but you do lose out on low end boost unless you have a variable speed ratio to drive your centrifugal blower. I'd imagine this would affect your on to plane performance compared with a coventional blower.
Variable drive ratio blowers are being developed (we're developing one at our company at the moment) but these are all being aimed at downsizing engines in the European market. eg 2-3l high boost and fast response.
Ruaraidh: When McCullogh first introduced the centrifugal blower that became the Paxton, it came with a planetary transmission that was downshifted by engine oil pressure when the accelerator was depressed at low RPM. This was necessary because the impellers weren't that good yet. The transmission was bigger than the compressor. As impellers improved the transmission was dropped.
I saw a two speed transmission for that small compressor from Denmark at PRI two years ago. Is that yours? Our problem is we would need the transmission to handle about 200 HP for our twin blower system. For us it makes more sense to put a transmission behind the engine.
We have put centrifugal blowers in boats that are going 160+ mph with one speed. You are not going to win a drag race with this setup but that isn't how the boats are used. Class 1 boats run between 4500-7500 RPM during a race. Poker run boats typically line up at 100 mph. In both scenarios low RPM response is not an issue. I would still like the transmission though.