The system seems to run stable until I put load on the multiport fiber adapter. I recompiled the entire operating system with no issues.
Try moving the adapter to another port. Also, some fixes went into -current recently fixing some em(4) issues. You could be hitting a bug.
Did you get serial working on your x4200 boxes? I tried not configuring the OpenBSD serial console and using BIOS redirection, that didn't work. I also tried disabling BIOS redirection and configuring explicit OpenBSD serial console support, but still nothing showed up when I connected to the remote management console interface. The only thing I haven't tried is physically connecting to the local serial port on the hardware itself.
If I remember correctly, only via the built-in serial port. You might want to get that working and provide a trace/ps when your system panics.
