I directed you to the dyno runs since I have no affiliation with Lunatik, we actually don't even really get along on the forums that much, so I figured it would be a good unbiased way to look at the engine performance.
But my side of the story, as it were, is this, the CY Marine top end is rated at about 4 hp with a stock style can, throw a pipe on , and that number starts to increase as the dyno printout showed (there is another series of dyno runs with the DS head kit and I think 5 different pipes), that is pretty damn respectable for all off the shelf, non- aftermarket ported parts.
When I started to work out this kit, I had consulted with Carlo from CC Racing Engines in New Orleans (holds pretty much all the RC boat records), and asked him straight up what he thought of the CY Marine top ends, he said they make great power, but they don't like to use them much because they did'nt seem to hold up for their applications, now keep in mind that their application is in a boat spinning at 17.5k for 5 minutes solid, never letting off, I ask any of you to find me a big bore, like a 30.5 that can even stand 1 minute of full throttle without blowing up, I think you will be hard pressed to do so.
Anyhoo, for the car applications, rarely will anyone peg the thing for more than a minute, so the reliability issue was not really an issue, and as I mentioned, I have been running many of these motors, 4 currently, with no problems, and I am about to start building a few more experimental motors with this same top end.
I don't understand the fascination with the 30.5 motors, they really are not all that impressive given the displacement and the inherent issues associated with running a 2mm stroker crank. I have been on the beach with many Baja's sporting the 30,5s and was not impressed at all, a few have been killer, but these are motors that have had extensive modification to them by people like ESP, so far from off the shelf.
IMO I think that the DS top end is by far the best bang for the buck, you can for an investment of $150 be getting a solid 4+ hp or much more with a good pipe, considerably less than buying a 30.5 rated at 4.0+ HP for $300 or 4.5hp for $425.
Thats my 10 cents, and yes, of course I am somewhat biased, however I have not heard of any issues or complaints as of yet with the performance of this setup, and I have been running one now for several months (since November) with no issues.
Hope that helps.