You should be able to press Ctrl+F11 instead of manually editing the config by now.
Also Dxtory shouldn't crash the game. o_o That and the fact that you didn't find the FrameTimeDisplay entry in your config really sound like you're just using opengl on stable. Are you sure you are on cuttingedge? If yes try the Ctrl+F11 thing and if it works make a screenshot right after some stuttering occured to you during gameplay.
Also Dxtory shouldn't crash the game. o_o That and the fact that you didn't find the FrameTimeDisplay entry in your config really sound like you're just using opengl on stable. Are you sure you are on cuttingedge? If yes try the Ctrl+F11 thing and if it works make a screenshot right after some stuttering occured to you during gameplay.