For the 757 you should plan to land with not more than 9 tonnes to avoid upper surface icing.
Ski destinations are probably less of a problem than humid destinations as you will probably be de-iced anyway and the relative humidity will be low. Humid destinations will cause condensation to freeze on the upper surfaces with more than 9 tonnes.
My company gives no guidance on 767s. Probably because it is unlikely you would plan to land with something like 24 tonnes.