You should be nitpicking; SSBM is not a demanding game, and your hardware is more than capable of running this game fullspeed without drops at all. Many (including myself) have done so with inferior hardware. OpenGL should not be causing you issues either.
You said you're using DX9, which implies you haven't checked out the latest development revisions. You should because these are noticeably faster than 4.0 in a vast majority of games.
You said you're using DX9, which implies you haven't checked out the latest development revisions. You should because these are noticeably faster than 4.0 in a vast majority of games.