Based on my experience, I wouldn't recommend a rogue at all in this game. I have yet to discover a single secret door in the game (that requires a rogue, anyway), traps do an insignificant amount of damage even when a character is struck by them, and any character with a decent strength score or a Knock spell/power can easily get into all of the game's locked chests and doors. Sneak attack just doesn't do enough damage to make up for the rogue's other shortcomings.
Because the game allows you to rest and recover all spells as many times as you want during an adventure, I'd kick the rogue to make room for another caster. A group comprised entirely of casters would probably dominate every adventure in this game with ease
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