Saying that using leaded gas will "foul" a catalytic converter is kind of an understatement. Lead kills the catalyst. Dead. You will not be able to pass any emission tests. Lead also leaves deposits on your spark plugs and will likely shorten the life of your O2 sensor. If you use Mobil1, note that synthetic oil will not hold lead in suspension as dino oil can. Unless you have upped the compression of your engine, 100LL av gas will not increase power or do any good thing to your engine.
I'm a chemical engineer by degree and worked in gasoline refining and specifically with catalysts. I'm also a pilot and use plenty of 100LL in my plane. I would never even consider it for my 968.
Lance