I have;

Ts) TrueNAS box 1 with SFP+ PCIe card
Te) TrueNAS box 2 with 10GbE PCIe card
Sw) Mikrotik CRS305-1G-4S+IN 4-port SFP+ switch
Ts connected to Sw with a DAC cable
Te connected to Sw with an RJ45 transceiver at Sw

Testing iperf3 between Ts and Te from the TrueNAS shell I only get about 6.5 Gbps.

Is it worth replacing the PCIe card in Te with an SFP+ one? Or is my bottleneck between the two boxes likely something else? Or would 6.5 Gbps be normal for “10 gigabit networking”? This is all in the same rack, no long cables.