Ive been testing my extended in opnsense with different nics, a week at a time actually running my network. Here are results so far if it helps anyone:
Supermicro aoc-sgp-i2 dual port i350= no issues best performance with lowest cpu utilazation numbers.
Built in realtek 8111, with 8111 card in the m2 a+e slot= no issues at all, 3 to 5percent performance hit vs a supermicro dual port i350.and cpu utilization was about 2 to 3 percent higher
Ibm branded Broadcom 5719 4 port nic= no issues, almost as good as the intel, 1 percent performance hit, and cpu untilization about 1 percent higher than the i350 dual port.
Next up as it just arrived, is a Silicom PE2G4I35L which is a 4 port i350 nic. Will test that for the.next week.
Having tested the Silicom card, it works great and works as good as the Supermicro i350 2 port card. No problems at all.
If you have an extended, using a intel i350 or if you cant find one at a good price, for 15 on fleabay a broadcom 5719 based card works well too.
If you have a slim 5070 and have to use the add on realtek 8111, I have had no problems either, you need to add the reatek plugin to opnsense for best performance. I noticed a slight performance hit and more cpu usage but for 1gb internet and less it works just fine.