I have a pair of RCV 60-SP's I'm going to run in a Martin Mariner flying boat when finished.

I've run them in, and they have a nice sound and certainly a small frontal area. The SP's, being geared 2:1 are very torquey and can spin a big prop (relatively). I'm using 13 X 13 four bladed on my 'boat'. The CD's aren't geared. Apparently the early models were very noisy due to straight cut gears, but I read that they are now helical cut, so much less noise.

I understand they need good cooling, so if you're cowling it/them, it is recommended that you have twice the outlet area as inlet in the cowl to get the hot air away easily.

They both start very easily.