100% smooth is the answer, when all is right.
I run greys, ported head, etc and it is smoother than me dads mondeo auto, smoother but not quieter, seriously can't feel any virabtion at idle.
I use V power and do find though that if I use a different fuel, even BP ultimate etc have the slight roughness, if I use esso it runs badly and flat, tesco 99 is next best for mine.
tabetha