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How long is a piece of string?
Depends what width tyre, the road surface (or lack of) and the weight distribution. Probably if you're on rear panniers then assume 35/65 front/rear, 45/55 if you're a front loading guy.
There's a plot here you can look at for suggestions on pressure based on those considerations. If you Google this topic (or summon @edscoble) you'll find many sides to the argument.
What pressure should one run Schwalbe Marathons at? The outfit will probably weigh 95-100kg including me.