I guess it's no huge suprise that the performance of these boards on Deboichet Customs fins is always going to be a bit better, as those are amongst the very best fins in the world. And yes, I agree, that some of the older generation production fins were not especially great at hi performance/hi load challenges..
However the iSonic fins for 2009 (retaining previous JJ Deboichet design - but updated for some constructional and process upgrades ) are normally doing pretty well in their test c/w some of the more exotic fins tested, and in some respects are quite good performance - even suprising us in testing. Like most hi end fins, the supplied standard fins do have some (tightly controlled) hand finishing processes, so it stands to reason that there may also be some variation (within range) over a batch.
Carlos, had you previously had an iS86 or similar and also tried the fin/s from that ?
Cheers ~ Ian