Aspect ratio has no effect in fullscreen mode. no point in messing with it anyway, the game should fill your screen and you will get the same aspect ratio that your monitor has.
Adjust your monitor to get rid of the black lines.
Scanlines doesnt have much effect on performance (it just blanks out every 2nd line for games that don't run in high resolutions). Directdraw may give you a speed boost, many people said that SSF runs faster for them in DD mode.
If you want the best performance, get a dual core cpu (core duo 2 recommended, Athlon X2 aint bad either, but its phasing out from the market).
Or to get rid of chopping, enable VSync and move to fullscreenmode. That way, every frame will be displayed with no frame skipping (much more fluid), but the game wont run at max speed. Your choice.
I've explained most of the options of SSF on my page:
SSF Tribute Neo