When its dry I keep my 25s and 23s at 120-125.
When its wet I ride 25s at 100-110.
When its icy I ride slick 37s at 70.
When its snowy I ride 2s at 60.
The retro grouches will tell you that running higher psi on skinnies is less efficient, increases number of flats, and is all around bad karma. Ignore them.