High Pressure + High oil temp = Using High HTHS Synthetic Oil IMO (Which you are doing by the way)
20 Weight oil is subject to burning off more at higher temps & you know what that burn off leaves behind? Deposits. The fact that a High quality Synthetic is being used minimizes this effect. Add in the HTHS of the 40 oil & it's capable of withstanding these forces/Temps better than a 20 weight. The numbers tell the facts.
Presumably you are using this car for more than just "Track racing" & there is a reason a 40 weight was given on top of the engine being used. You're seeking longevity with some track days. If you were seeking every last HP & a track only car that you didn't care needed to be rebuilt sooner then you would see a 20 weight.
That being said I doubt you will see any difference in your situation since you have run thicker weights & use this on the street also. It won't grenade by using a 20 but use it for long enough & keep this car long enough it could start drinking oil more on a 20. Will this get you till the end of your ownership... Probably so you'll never really tell the difference since there are not 2 simultaneous tests going on. Throw in the fact that we'll never blame ourselves for the visc of oil we used. lol
Bottom line is that the 40 weight has the potential to stay intact rather than burning up more than a 20. A 20 may contribute to deposit formation vs a 40 from the burn off.
Anyways, I really enjoyed watching the video & it's great to see man/machine still doing what we've been doing for many generations. This is the right place at the right time. My speeding ticket days have been over for a long time lol A track takes that out of the equation. Seeing the specific track on the screen is helpful. You were flying in some of those straightaways.
This is my xx-30 Viscosity version (Opinion)
20 Weight oil is subject to burning off more at higher temps & you know what that burn off leaves behind? Deposits. The fact that a High quality Synthetic is being used minimizes this effect. Add in the HTHS of the 40 oil & it's capable of withstanding these forces/Temps better than a 20 weight. The numbers tell the facts.
Presumably you are using this car for more than just "Track racing" & there is a reason a 40 weight was given on top of the engine being used. You're seeking longevity with some track days. If you were seeking every last HP & a track only car that you didn't care needed to be rebuilt sooner then you would see a 20 weight.
That being said I doubt you will see any difference in your situation since you have run thicker weights & use this on the street also. It won't grenade by using a 20 but use it for long enough & keep this car long enough it could start drinking oil more on a 20. Will this get you till the end of your ownership... Probably so you'll never really tell the difference since there are not 2 simultaneous tests going on. Throw in the fact that we'll never blame ourselves for the visc of oil we used. lol
Bottom line is that the 40 weight has the potential to stay intact rather than burning up more than a 20. A 20 may contribute to deposit formation vs a 40 from the burn off.
Anyways, I really enjoyed watching the video & it's great to see man/machine still doing what we've been doing for many generations. This is the right place at the right time. My speeding ticket days have been over for a long time lol A track takes that out of the equation. Seeing the specific track on the screen is helpful. You were flying in some of those straightaways.
This is my xx-30 Viscosity version (Opinion)
... Looks to be that Ted got some Liquimoly Leichtlauf High Tech 5W-40 bulk oil to teach him a lesson. What Ted didn't divulge is that those pulled engines were being rebuilt because he thought 0W-20 was "good enough" for the previous track use. 
