Is this a 3000GT VR4?
This will go against everyone on here but it's my own experience... With the GN, I've had best luck with conventional 20w50 with bearing and ring wear. This is with multiple tear downs that I personally did all the measurements before and after, and 1,000 mile or sooner changes.
Take it for what it's worth. Not sure about your motor, mine is a high torque, high boost, relatively low rpm motor. I think the thicker oil could possibley help if you get a little greedy from time to time with the tuning like I tend to do.