For the crank, My first 951 engine build, I sourced out and OEM crank with Racer's help. I've since sold the ski but it has been running great with 30 hours and has come back for me to winterize it.
The second I did for a friend and he went cheap with WSM crank. He's put 50 hours on it since last year and LOVES that engine. It runs really well. And he doesn't baby it being in an 01 xp! Probably spends more time under water or bouncing off the rev limiter than anything else.
The engine in my xp was built by my parts guy with SBT parts. (for 1000$ and no core I couldn't go wrong) Honestly it's been running beautifully. It was having a problem starting cold. but that has nothing to do with the engine.
So the choice is yours. Honestly the OEM's may last a little longer, but the 951's life is normally cut short due to CB shaft failiures, so it doesn't matter what crank you have, if the cb bearing goes. it will take out your crank. So I would be focusing more on the cb shaft. Both engines I rebuilt used OEM bearings (Had a shop press off the counterweights, etc) just my 2 cents.