Actually the RL 0W-XX oil range is just one oil with different polymer levels to make up the three grades. The 0W-20 contains no VIIs, the 0w30 just a pinch and the 0W-40 a fair amount but it's still very shear stable. So it doesn't matter if you use the 0W-20 or 0w30 in blending to acheive an oil with a HTHSV between 3.2cP and 4.0cP, the VII content will be the same.
BTW, RL 5W-40 is not a grade I would buy, not just for it's lowish VI but also because it contains no moly; it's really a deisel use oil.
BTW, RL 5W-40 is not a grade I would buy, not just for it's lowish VI but also because it contains no moly; it's really a deisel use oil.