I don't think they are now - I've got SR cometic and Cosworth gaskets and they're definitely different. The Cosworth one has a thicker section around the bore, presumably to give a better bore seal.
Not sure if these guys will do you a 100mm VQ gasket: http://www.powerenterpriseusa.net/produ ... asket.html
We use their 90mm gasket on our SR - that's been making 600bhp with no gasket probs at all. I know Mazworx use the same gasket for their 1000bhp+ drag SR.
I've heard of (but never experienced myself) Cometic gasket failures.
I think your right mate the cosworth has a folded stopper layer cometic i think dosen't have that ?.