[tor-relays] Reliable way to gauge tor throttling?

[tor at t-3.net]

Assuming the Tor service is running on a dedicated host, you could use 
an SNMP-aware switch and query it with Cacti for graphs on the 
switchports, or maybe run an snmpd on the node and use Cacti to build 
graphs against the node's ethernet card stats.

http://www.cacti.net . It can also be pulled down as an RPM from some 
repositories, such as epel.