Convex or outside.
In that case and if you want to go with the scoring route if you can't find the other stuff - use a dado blade from the back side to create some space for the inside bend. (I can't visualize the radius of your curve - but believe me, drywall bends fairly easily - even a bundle of 14s half-inch will bend about 15 inches end to end without any more help than a "board-packers" shoulder into it. You can get about a a 45 degree overall from dry 1/4" without doing anything.
Back then Westroc used to have more give than Domtar, but it's probably been reformulated a few dozen times in the past 14 years.
Bren R.
