Rob, I only have experience with the Butler small bore gaskets. I sold a couple sets of the big gaskets at the Nats last year while at the IA trailer.
I have nothing against Cometic, in fact, I hear alot of the NMCA guys run those gaskets.
When I visted Ken Keefer last summer at his shop, I mentioned that I heard Cometic was making gaskets for Pontiacs and even e-mailed him the link when I got home. Of course, at the time, there was nothing available, but I had heard through the grape vine that something was coming.
Whatever Rodney Butler is running to hold his 2200HP, 30psi twin turbo motor together is what I'll be using to hold my twin turbo motor together.
Chance favors the prepared mind.