My game is somewhat similar to yours. Unhindered I get 100-200fps, but I lock that down to 60. I'm not sure what I'm doing differently than you. I use lots of DrawText (all text on screen is DrawText) and I draw 5 layers to my scene, plus the GUI on top.
I know that OpenGL is just plain faster. You may want to default to that and if the Graphics mode can't be created, fall back to DirectX.
I know that OpenGL is just plain faster. You may want to default to that and if the Graphics mode can't be created, fall back to DirectX.