I went with the Cometic even though I didn't SC or turbo it. I don't have plans to.
I may never know if it was a good or bad idea, but I went with what I hoped to be a better than OEM part. I also used the Opel studs from ARP. Again, for a small improvement on a great design.
If there are any pitfalls to under-using the Cometic, I'd sure like to know. Corrosion issues? Leakage?