It's true, my old SP4S runs a helluva lot smoother with Ultimate or Optimax, quicker warming up and no coughing and hunting when cold.
Add a touch of octane booster too and wayhey!!!
The exhaust note is different too, not only do you get the deep rumble but also a sharp crack like a highly tuned two stroke note mixed in.
Sounds fanstastic.
Ains.