Also how much would 23mm tyres improve things on a 10?
Don't you check your tyre pressure before a TT? I check mine before every audax, FFS. Mind you, that's mostly cos the front one seems to lose pressure quite quickly in the garage. I usually ride at about 110 - 120psi, but I've really no idea what the optimum pressure is.
You are not using latex tubes are you? They will lose 10psi or more overnight.With light tyres, and especially latex tubes (or tubulars) it's a good idea to let them partailly down after each ride anyway.