as far as I remember, the Upat bolts are machined from stock. The Hiltis are cold rolled [ a form of forging where the thread gets rolled into the shaft, and the shaft is shaped in this process). The machined bolts are more prone to SCC due to tiny pits being left in the bolt which is a breeding place for rust and corrosion to start. I stopped using Upats after a batch I bought had some dodgy threads that were weak and stripped easily. After that it's Hilti all the way. There is no reason not to use the best quality when it comes to route setting.
I think if you're using express bolts in coastal areas you're just wasting your time and potentially putting other climbers at risk. For a place like 'boven, you don't get a better solution than a 70mm Hilti express bolt, but for coastal or soft rock conditions you're better off with using glue ins with a good compound. That said, a glue in is only as good as the installation (any mistakes during the setting can render it a dud), thus often an express will be more safe in the short term.
I must mention this though, the drill bits from Upat are the longest lasting bits I've ever had.