USRP2 metric measurement

Hi,

I need to measure any metric(say RSSI) of one USRP2 from the other, to
implement a selection scheme that selects best USRP2 based on best
metric.

what best can be measured to estimate the quality of the link.
All comments/suggestions are welcome
I am using gnuradio 3.5, on fedora 15.
USRP2 with WBX daughter boards

Thanks,
rafiq