The prop pitch can make pretty big difference on dive, cruise & climb speeds if one knows how to use it. Then again, it is different for all the planes, so you really need to either go by trial & error or study the plane via documents & flight manuals.
Here's the prop pitches for the 190
http://mission4today.com/index.php?n...p=show&kid=308
EDIT: The common use I've seen is <80% in dive, >80% in climb.