My Clocked P5 beat every engine at the race yesterday on the straightaways, even O.S. Speeds. Puts down power fairly smoothly, get the truggy mod for your SC8 and you will have one monster SC8.
If you don't want to spend the extra on the clocked P5, get a stock one.
If you want that Novarossi Roma .25, get it, its a beast.