Just wanted to add my short experience with HPS 10W-40: I have a '13 Citroen with a 1.6 litre diesel-engine. It's known to be a reliable engine but with quite some diesel-knocking-sound. Same engine is used in several brands like BMW, Peugeot, Ford and Volvo's. After last service at 40.000KMs/25.000M (still in warrranty, so I have to let the garage change oil to their original Esso-something), I replaced the brand new Esso-oil to the HPS. No big imidiate change, but after a few days of driving the diesel-knocking is pretty much halved, MPG is raised from 48 to 55 (5.1l/100KM) on equal conditions. What surprised me most is the power gain: In our daily route we drive a steep hill where I used to maintain speed at 90KM/h / 55Mph with flat pedal in 5th gear, now it slowly raise to 95-96KM/h / 59Mph, at equal conditions.
The numbers is pretty much the same as I have seen on my other cars (and motorcycles for that matter) when changing to RP from dino-something, but it surprised me that I got this numbers on a new and modern, low-friction engine.
BTW: Here in Norway I pay approx $20/quart for this, while i.e. Mobil 1 ESP 0W-40 is $29.