I run Shell Rotella T 15W-40. My oil guy seems to think that I can get away with a 30w so I may try that next year to get my oil pressure down smidge 60-80psi (either that or my gauge sucks).
Synthetic is great, just remember that the engine manufacturers state that even if you run sythetic you should not use that as a justification for extending the drain intervals.
1992 Supra Mariah - Red
PCM 351HO 285hp - PCM 1.23:1 Transmission
OJ XMP 4 Blade CNC 13x15.5RH
"People do weird things to boats" -Unknown