I'm relatively new to bikes so I might be talking out me arse, but shouldn't you follow what the manufacturer says for tyre pressures? If you run with 36/42 (pillion and/or luggage pressures) when you don't have the extra load, the tyres wouldn't be under as much load and would be a different shape to that intended? I would think that the tyres deform under pressure and the trick is to match the tyre pressure to the load so that they deform by the right amount. If the tyres were over inflated they wouldn't deform enough and you would end up with a smaller contact patch on the road? Also doesn't it make the ride a bit hard using the higher pressures with no pillion?