Everyone has diffrent views on this. The new scat cranks while cast are very strong. They can take on heck on a beating. However in this case I would have to say it would be best to go forged. Spinning a cast crank up to 7 grand is going to push it. TThe main reason why I say this is because of the added juice. Some forged assm. say they will take 200 shots.
In other words if this engine is going to see lots of high rpm use and have shots of the juice for the simple fact of keeping the beast alive I would go with fogrred internals. BUT thats just me!