My UDM Pro seems to top out around ~800mbit per UDP stream - pegged at 100% CPU on a single core. Likely it can't keep up with the interrupt rate, given it's ksoftirqd pegging it. Replaced UDM Pro with a pfsense machine.
Then I started getting 100% packet loss on the edge of Frontier's network after a couple of minutes of sustained UDP near-line-rate throughput. In the end, after trying and failing to explain this to Frontier's tech support, I reached out to their engineering management on LinkedIn, and got put in touch with the local NOC director. Turns out to be some intermediate hop is rebooting after a few mins, and they're "in contact with the manufacturer". Haven't heard back in a few months.
tldr as >1Gb connections become more ubiquitous, other bottlenecks will become apparent!