So Im building a 5S with 3S head.
Ive had a lot of custom machining work done including matching of the water channels to the head and also 4 individual water inlets per cylinder for more even cooling.
My goal is to run in the region of 650-750hp with a FMW S300.
I am questioning the strength of the 5S as many people seem to only go around 500-550hp and not exceed 600hp.
Is it worth wet sleeving it?

so they say the 98+ blocks are more stronger. personally its all in the tuning. a good system and good tune and you will be just fine.