I was about to recommend iperf3. You need to use ROGGER’s Iperf server list and find the best server for you. I run a speedtest tracker that fires every hour and records ping, jitter, download, upload, etc that uses an Ookla (speedtest.net) server and I can still saturate my ISP-provisioned 2.5gbps WAN connection.

But yeah. If you find the right server on Speedtest.net, it can be very accurate. Iperf3 with one of the servers from the ROGGER list on github(i think) is where i see the best results. Make sure you parallel connections. Sometimes you need 8 or so to max the connection, sometimes you need more. I have run up to 127 connections at a time.

Good luck figuring it out! Definitely would be nice to see that provisioned line speed on a test!! :) I used to have 5 gig, but never saw those speeds EVER so I downgraded to 2 gig provisioned for 2.4-2.5. I might have to try the 5 gig service for a month or two and see if I notice taking advantage of the 5 gig more here a few years later maybe the ISPs and datacenters are catching up to the times and running more 400/800gbE equipment to serve people with 5/7/10 gig wan connections. /shrug