Not in that same application, but our local porsche club has a lot of guys that run Amsoil motor oils, and race on them with success.
What speccs does it call for? I was always under the impression that the GL4 fluids were better for brass. Porsche may be different.
....I did a quick search on the Amsoil site, and it looks like theyre suggesting the OEM fluid be used. On that car, at those temps, I'd be hesitant straying from factory fill.
Just my 2 cents, but it's only worth that!