Mostly, latency and packet loss in nodes will negatively impact Tor's usability. . .

Was reading this thread and thought of potentially useful and perhaps not overly difficult BWauth enhancement--perhaps worth considering as part of ongoing efforts to rework the BWauth scripts.

When measuring a node, a BWauth could spawn a 'tcpdump -w' PCAP capture of the specific test connection traffic and SIGTERM it when that's finished.

Then run some tool or another to analyze the connection for SACKs and/or other indications of the quality of the relay and path.

Here's one example:

https://github.com/lennart-schulte/tcpdump-analyzer

Alternately, such a mechanism could rely on a continuous 'tcpdump' running with a large circular buffer and a script or program could follow the test connections and spit out a statistical summary for completed ones to a text log that would then be consumed by the BWauth scripts.

If the idea has potential, someone could perform a casual passive 'tcpdump' of test traffic and examine a few connections.