I'm shopping around for 75w90 gear oils for my C7 Corvette and am noticing that many of the well-regarded or track-focused products (Gear 300 LS, Amsoil SVG, Delvac 1, etc.) have very low VIs...usually between 140 and 160. Why are these so low despite being synthetic formulations? By comparison, Renewable Lube's Bio-SynXtra 75w90 has a VI of 187, I suspect due to its KV @ 40C being an impressive 90cSt versus the above fluids which are all 100-120. As an aside, I find it odd that the non-LS version of Motul Gear 300 has an insane VI of 222, again due to an even more impressive KV @ 40C being 72.6cSt! Is RLI's fluid really that much better due to its naturally high-VI basestocks, are they using VIIs, or is there something else at play? At a glance, it seems foolish not to take the RLI.