It will hold 541 at DB, and 628 at MAP.
I don't think you can just slap numbers to these things. There's so much more involved. If you slam through gears hard, dump the clutch without pre-loading the drive train, beat the hell out of it, well then even a shep stage 2million might not last an extremely long time at 300hp.
A 4-spider will definately be a good step at helping it to reliably hold more power though.