Hi @jonathanj,
The specific test results that I posted here were from a desktop machine with a wired connection to my router. However, as I mentioned in my initial post, I performed a similar round of testing with my computer hard-wired directly to the modem. While the results were marginally better, the 1mbps difference was small enough to be attributed to standard network overhead.
I have run numerous tests on speedtest.net, specifically choosing servers which were geographically distant and NOT hosted on the Cox network, and results achieved through speedtest.net and fast.com consistently show results in the neighborhood of my plan's 150 Down/10 Up rates. I also specifically ran several tests to the BayNIC speedtest server in Fremont, CA, which is hosted in the same Hurricane Electric datacenter as iperf.scottlinux.com, the public iPerf server that I have been using to run my iperf tests.
Regarding iPerf and iperf.scottlinux.com, that server is confirmed to have at least 1 Gbps upstream and downstream, and in running off-site iPerf tests outside of my home network (i.e. via the T-Mobile network and my work's enterprise network) I have consistently been able to achieve upstream and downstream results to that server well above what I see at home, indicating that there are no bottlenecks on the server side.
Note that iperf is just the best tool I have found to specifically test speeds outside of the widely used speed test platforms, but the upstream results I see via iPerf are consistent with the transfer rates I see with real world loads such as Plex Media Server streaming, syncing to Google Drive, syncing my devices remotely via Syncthing, or performing large file transfers over an OpenVPN connection. Under all of these loads, my upstream transfer rates are consistently in the range of 2.5-4.5 Mbps up
I should also note that neither I nor the Cox support rep that I spoke to on the phone have found any evidence of packet loss on my modem, and in the past I have been able to consistently achieve 8-10 Mbps upstream using my current hardware configuration, so I am increasingly convinced that this is not a hardware issue on my end.
If you have any additional suggestions for further troubleshooting, I am all ears.
