Guess that switch wasn’t too keen on trying to split the packets evenly.

Yeah probably, I was just using one of those cheap 2x 10G + 4x 2.5G switches that ServeTheHome recently did a video on, so I would not be surprised if that was the bottle neck here.

I could maybe try buying a few more SFP+ transceivers and using my more trustworthy switches, but that seems too expensive for a project like this.