Brad Penn Oil

You want the lightest lubricant that will do the job. So long as the bottom end clearances are close to stock 10w30 is a great choice.

Oil pressure doesn't mean the engine is getting well lubricated!!! Think about it, the oil pressure tap is pretty much upstream of everything. If you blocked all the passages at the bearings, you'd have great oil pressure on the gauge. Also, by definition viscosity is resistance to flow. Flow is a good thing.