Have not tried using Linux yet but hopefully will soon and see the speed I get on iperf and @RSR what hdd are you using at either ends of that connection?
Desktop: Samsung 970 EVO 2TB NVMe / Intel X550-T1 NIC
FileServer VM (Server 2019) which runs on Dell Poweredge T640 - 6x1TB MX500 - RAID5 (Dell Perc H730p) running VMware / Intel X520-DA2 NIC.
I do also have a Synology DS1618+ which normally tops out at around 500MB/s but that's being replaced soon by a FS1018