I wouldn't use anything thicker than 10w-40 in my B18. That guys running 0w-60 or whatever in his NA B16 is a nutter. Yes there is better protection, but less flow flow. I think you would spin bearings if you rev hard on a track using that stuff.

5W-30 is fine for the street, even in hot, harsh aussie climates. If you are scared it's too thin... then use 5W-30 for winter, and 10W-40 for summer.

Mineral oil is fine too. Just need to change it earlier.