LDH is muted in his reply.
There isn't a tire out there that displays its best performance at the OEM suggested pressures.
Legal paranoia makes them state the pressure that provides the max load rating of the tire, regardless of what bike it happens to be on, let alone details how heavy the payload is.
42 in a rear in cold weather and on a hard sidewall tire is like being on a corduroy road.
OK, enough of my ranting.
I'm running Michelin 2CTs on my 919, and had Michelin Roads on before.
For solo road riding 31/32 in the front, 35 in the back. I weigh 170 # before gear.
When I have my wife on the back, I bump up to 33 front 37.5 to 39 in the rear.
If we were to tour, with lots of day long straight up miles on hot pavement, rear at 40.