Flashpoint seems low for an oil with only a trace of fuel. I thought Blackstone calculated flashpoint from fuel dilution, so this seems a bit odd.
If the shearing is of concern, you may want to try Mobil1 5w/30. Pennzoil synthetics tend to be on the thin side, Mobil1 on the thick. In 5w/30 The "old" Platnum's 100C Cst is 10.4 vs Mobil1's 11.0. The new formula Platinum is thinner still. The oil will likely still shear, but may be more likely to stay in grade.
And I suspect Blackstone meant to suggest trying 10,000 km next time rather than 10,000 miles.