Shameless self-promotion ahead...
This is more a suggestion to help with mapping received signal strength (RSSI), rather than data network latency and bandwidth (you can argue that those data network metrics rely heavily upon your RSSI!):
Grab an old Nokia, use gammu
to enable Network Monitor mode
, fire up a GPS and display the combined information streams on a map. I did exactly that as an experiment
using a Nokia 3310 and a Navman GPS receiver. Interesting to then correlate the signal peaks to the actual base station locations
The main caveat is that the old Nokias in question only do (I believe) dual-band 2G GSM at best, so you won't actually be able to measure 3G W-CDMA statistics as if you were connected with a 3G data device. I would offer, however, that 3G RSSI might be related to that of 2G as many of the base stations handle both services (ignoring differences in signal propagation characteristics).
A starting point at least...