SNES: Stunt Race FX. Not only did it require the external FX chip, it still ran like jerk-o-vision. Contra III or Yoshi's Island are peanuts compared to Stunt Race FX. Contra III in two-player mode would sometimes slow-down and get the disappearing sprite artefacts but SR FX ran slow all the time. Play it in two-player battle and prepare to be declared legally insane. You'd see 20 polys, flat-shaded and still get below 15fps. The SNES just wasn't meant to handle SR FX. My second, distant, choice would be DOOM.