thats stuff I gonna test!
does it really save power swapping networks from 3G to 2G or even off, what is the benefit and for how long needs it to be turned off/swapped to really save power. Negotiation needs more power then keep-alive-pings.
I would concentrate on things that run all the time, like timers watchdogs daemons first. The in anycase powerhungry connections come after GSM for me, if I want to use it as primary cell phone this is always on too. only internet connections like xG and wifi are left then and there the benefit calculation/measurements come to play!

Set Away after 5 but don't do N/A in 15, powerdown the network-connections instead?