The stock bottom end can deal with a lot torque for what it is.Knock,detonation & pre-ignition are homewreckers which behave like a slap rather than a push.A boosted engine with normal combustion has a rounded cusp on the component load curve vs a pointed cusp on the load curve for an improper combustion.Castings are subject to inclusions and a finite performance endurance limit.Some castings may have fewer inclusions than others.Castings will not live forever.Some folks are lucky and their castings live under high load a long time.The rolled fillets on the cast crankshaft are a life saver.Balancing the stock components will lengthen their lifespan and assist their abilities to deal with load.Balancing reduces/eliminates undesirable vibrations relating to both how well the engine "builds" and reduces tensile & compressive forces.This is done through lightening the heavier connecting rods and pistons to the weight of the lightest one.Maybe lighter wrist pins etc.Elimination of stress risers on components reduces component fractures.Weight reduction & balancing will allow a few hundred more rpm.I'm not convinced that the stock "SPS" rod bolts can't handle the tensile loads of the stock piston flying around at 5600 rpm.Stock casting failure is directly relative to 1) improper combustion, 2) unpredictable inclusions/fractures,3) the finite performance endurance limit of a cast component has been exceded.This is done by increasing loads for longer durations of time.Castings accumulate their loads and eventually fail.I don't think a stock bottom end will fail at the 500 hp level "for a while" provided combustion is controlled and you're lucky.There have been those people with gutted cars and great castings that have run 10's for a season.These folks are the exception to the rule.