Regarding tire pressure for above 200 km/h, I just read the following in Paul Frere's Porsche 911 Story: "... it is interesting to note that in his speech introducing the 911 S to the press, development engineer Bott mentioned that part of the gain in maximum speed was because of the increased tyre pressures recommended. [...] It appears that at the car's maximum speed, the reduction in rolling resistance amounts to a saving of more than 9 hp -- at the obvious cost of some comfort."

I would have expected that the higher pressure was to have better handling at speed, not to reduce the rolling resistance!