M1 FS 5W-50 is a solid choice if you want something stout in that flavor. But I'd definitely pick Delvac Extreme 15W-40 or MX 15W-40. An oil is more than the sum of its parts, so skip looking at base oil and giving it more weight in your decision.Car is turbo diesel, 5500rpm, getting on for 180bhp/L, and 1000-1100nm. Driven hard daily. OCI approx 5k miles (max 7K).
You might want to look at these choices as well:
Amsoil ADP 15W-40
Mobil Delvac Modern Super Defense 15W-40
M1 15W-50 if it's available
Mannol Favorit 15W-50 is also a good performer.
I'm just concerned about ensuring there is sufficient oil film maintained on the bearings. I will do some more reading, but I was thinking to chose an oil with higher Hths and of better base stock to help achieve this under hard use.
This figure applies for normal driving conditions. You stated that you drive hard, so pick up an HT/HS at 3.5 or higher for a cushion.
HDEOs more often than not have less viscosity index improvers because they are formulated from higher base oil viscosity, meaning they offer better hydrodynamic and mixed lubrication and contribute to less deposits and sludge formation. HT/HS is irrelevant in full shear regions in engine and base oil viscosity has full effect. The term HT/FS is coined by @Gokhan and is discussed more thoroughly in his posts.What else am I missing that makes the HDEO more suitable over the Petronas type oil?
CAFE practise their favorite hobby to a lesser extent on diesel engines OEMs and this reflects on HDEO as well. Better protection. Less restrictions on viscosity, AW, and emissions.
And your engine is compression ignited, so pick something that serves this application. I'd use HDEO in gasoline engine, not the other way around any day.