In my experience there is not "one size fits all" best valve cover gasket for the turbo Buick.
First, the are different heads, iron and alum, and they have different sealing surfaces.
Then there are MANY different valve covers that are machined different than the factory one. Also, the different brands of gaskets, even though the same material, style and composition will vary.
The different uses of cars must also be considered as street and strip has different conditions - higher boost and more frequent removal.
Installation procedures for various gaskets vary.
With all that said, here are a few "things" I have found:
The perma-dry will not seal well at high boost, and have seen many blow out and leak at the track. They also do not work well with the TA low profile VC because the way the lip is machined.
RTV and silicone do not seal gaskets, especially rubber, well over a period of time. [Remember our summer heat is MUCH hotter than almost any city area.]
Cork gaskets require a "re-torque" during installation, and after a heat cycle or 2. When installing a cork gasket, the best method I have tried is to use spray adhesive to stick the gasket to the VC.