I'm not surprised to hear 50Kpsi on a rail pressure spike at all. I've spiked my rail pressure on the dmax to 42kpsi when I'm changing things and am working on dialing in the tuning. Its just a spike - but that spike is what splits things - blows the tops off of injectors, etc.... rail spikes in common rail applications and tuning is nothing new. if he can't get them under control with tuning - then some mechanical parts need to change. There is a reason that these systems run blow off safety valves - the trick is to make sure the blow off valves need to be sized to dump enough fluid to control the spike.
NOTE: I have no idea the details of Swamp's setup - they may or may not have a blow off valve or other things they are trying to do to make this work.