Hi,
94supraonchrome - The Porsche Approved and Listed M1 0W-40 is very hard to beat in your engine. The lubricant plays a real role in engine cooling as you know - it is not a case of "thicker is better". Only one SAE50 lubricant is Approved by Porsche - M1 5W-50 and that is not available in the US
I use the equivalent of M1 Turbo Diesel Truck 5W-40 in my M96 engine and it would be an excellent choice in yours - it has a great ability to handle high temperatures for extended periods with no loss of viscosity
do check out Castrol Syntec 5W-50...i know peepz with high end cars singing praises...do check it out if it something meets ur car's specs.....it is SM rated as well as GF-4! and you know Syntec is very widely available
Amsoil products are mostly very very good
and GC 0W-30 is approved by a lot of high end and euro cars...my personal fav!