What's the Difference 4" Stroker CRANK??

Just reading the links - the lightweight crank has machined/knife edged (lighter and less power lost to windage) counterweights. That might an issue if it's being internally balanced and heavier H beams are used. The others are the same crank, with heavier (unmachined) counterweights that's marked up by MP. I personally have not used the Scat lightweight but I wouldn't have a problem doing so in a street/strip application under 600hp assuming the bobweight allowed for internal balancing. Same limits as the MP cast units.