With IB you can test by going to
Start->Run type 'cmd'
then type
ping gw1.ibllc.com
I'm having 300-400ms with a 3G connection
I get the same with 15Mbs ADSL on a good day, bad days usually around 450ms. Above that and I do a -n 100 test and call my ISP with the result.
Swing trade, so I don't care too much but as I just discovered when packet loss gets too great, IB servers repeatedly disconnect.