I know, this is technically a late response....
To find out what speed your network card is set to (10 vs 100 vs 1000), you can check Apple System Profiler under Network Overview.
For simple pinging and traceroute tests, try WhatRoute and OTTool.
For performance testing specifically, I think I once read of a version of iperf2 that is ported to Mac OS, while looking for the Windows 9x port. I'm interested in doing some NIC stress testing myself, I just don't have the right moment to look at this too much, quite yet.