I find people in north america get too hung up on the XPS vs. PU specs. Yes, there are differences in both foams, many of them are already mentioned in the posts above. Composite panel construction has been implicated in the commercial trucking industry all over the world (except in NA) for more than 30 years. In fact, I just got back from a meeting in China with our Australian customer (one of the biggest truck body suppliers in AUS). For them using composites is the norm and they would never consider anything else. Therefore it's not "new" technology. 99% of those commercial trucks and Expedition Trucks are using PU foam cores without issues. Or at least with minimal issues (after all, anything can fail...)
In any case, here in NA private builders go with XPS because it's easier to buy. All other points are valid but wont really make the panel better or worse if done correctly.
For me personally, I would never use XPS as it's not easy to work with when you need to do repairs. XPS will desolve with most chemicals/resins.