definately full synthetic. if not for the additional ponies, then do it for the additional protection. conventional oils are supposed to be good for ~3k miles while synthetics are said to be good for ~6k-7k miles. also synthetics can handle extreme conditions better (ie overheating etc) and don't break down as easily so they'll leave less sludge in your engine.
FWIW when i swapped my whole drivetrain for synthetics the difference was HUGE. the car pulled harder and smoother.
-steve