My money would be bet on the Havoline synthetic as an all Grp III formulation. This is probably a Grp III base oil in the 6-8cSt range, with pour point depressants, to meet the 10W rating.
The Chevron 7R(7 cSt) Grp III base oil, alone, has a flash of 250C/482F. Additives & carrier oils can boost the flash point up to the 258C/496F range.
Comparable Grp III synthetics are Valvoline Synpower 10W-30 with a flash of 250C/482F and Citgo 10W-30 @ 252C/485F
But, the Havoline synthetic Noack number of 5 is really outstanding, as these comparable Grp III's are in the 8+ range!