Apparently when you go much lower than a 4.x base stock, volatility climbs substantially. Bruce cited this as a reason why he's pretty much on the floor when talking about an every day PCMO with any kind of longevity in use in our 0w-10 distractions.
You're limited on the physical amount of additives that you can add due to how much they alter the end blend visc. They're all packaged in their own carrier oil at a concentrated ppm level. So, if you need MEGA ADDITIVES and need to "make room" for it in terms of a lower base stock, you're going to have volatility. Not so much an issue for 5 qualifying laps.