It looks like your relay could be CPU-core-limited, or limited by some other
local resource, or limited by its location.
Currently the CPU is only using 40% of 1 core (out of 4). All of it from Tor when BW is close to 250Mbps
When routing from the LAN (iperf, downloading stuff etc) the machine easily pushes 500Mbps.
It can of course be other local resources that Tor needs. I have set a lot of networking parameters in sysctl.conf many years ago (from torservers,net I believe), but I don't really know what all of that stuff means.
As to limit by location (Sweden), not much to do about that :)
To work out where the limit is, run another Tor instance.
You could also wait another week to see if your relay picks up another 5-10%
traffic increase.
I'll wait a bit longer to see what happens and then run a second instance.