It's a tricky one Tony. (like everything in motorsport!
)
Higher pressures can dissipate heat better as I remember it, but you've obviously still got to balance that with the fact the tyre will heat up and further gain pressure as it's used. So it can be a fair bit of work getting the right 'hot' pressure at the end of the process.
Think (will check later if you like) I had pressures ranging from 35 to about 40 psi for that race and ended up with good balanced temps still at the end.
I think I normally end up with the cold pressures in heavily used tyres being higher than unused tyres