To answer the original question (My opinion)... I think you don't hear much about these conversions because there are VERY FEW that actually are running and even fewer that are running WELL. Those that jumped on the bandwagon thinking it was the way to go either never got it complete due to lack of parts or frustration in getting it all together and running.
Lets face it there is NO good exhaust solution to date for this setup. Sure WDK has their wet and dry pipes if you can get your hands on one and then will it hold together once you do get it? The manifold that Demon & Tom21 were working on might have been the answer, but it is dead in the water...
Performance... 66e's are HEAVY, both in overall weight and in flywheel/crankshaft weight. So they do not spool up quick like a 62t based platform... Unless of course you step up to total loss and a specially lightened crank - but who's doing that on a "budget"
All this being said, I know there are a select few people out there that have put the time and $$$ into these to make them work well (such as superramjet & WDK/Ski Clinic) and they can be incredible. I just dont think they are any sort of inexpensive big-power solution for the average rider (and budget).
If there are truly a bunch of these out there running well... please prove me wrong and post in this thread... let's see pics and tell us what pipe & ignition you're running, and how does it run?
(I don't think we'll see many responses)