I think that backcountry ski pants suit the needs of covering both aspects of skiing. Backcountry skiing is all about compromises and ski pants are no exception, and also may cost as much as downhill and XC pants combined.
I have relatively good tolerance for cold, so my solution is to use jus a shell-type pants (i.e. with no padding for warmth) with zippers that run down the side of the leg. On cold days I put smartwool underwear and partially unzip the side zippers on the way up. On warmer days I'd skip smartwool.
Hope this helps.