Im with ya bud. Where's the best place to get a spare.
3 blades from what I've heard are faster on the top end on most boats. Just lazy out of the hole and can blow out in turns
4 blades are better out of the hole and don't usually blow out in turns. They give you more lift and cruise at slower speeds at similar RPMS than a 3 blade. However, top end is usually less. They also have better load carrying capacity versus a 3 blader.
That's all I know.