IMO its apples and oranges. Synergyn doesnt come in 5w40, or a 40 weight at all. Synergyn is mainly a gas racing oil, but can be used in diesel, D1 is a diesel that can be used in gas.
I have 5 gallons of SYNERGYN 3/30 and wondered when you said its a racing oil do you mean like M1R. I was hoping to use it for hopefully 5000 mi during the winter.