A friend and I have started an ALL Rad/* SG on the Virtue server, Fallout Shelter, if interested send a tell to Chernoble.
/end shameless plug
Actaully EF is a rather endurance heavy toggle, for the levels with out Stamina I suggest going RI due to it's not that END heavy. Also if you want to be able to have Perma-AM you are going to have to get AM slotted with 6 Recharge, and maybe a 4-5 slotted Hasten, that should give you Perma-AM and Perma-Hasten.
Also with 6-8 AM stacked all you should need is Tactics, it's like putting SO Acc in all your attacks (unslotted)
I was running around with a group in Steel, the team was all Rad/* defenders and the team was a: 11,9,7,7,6,6,6,5 and we were defeating lvl 13 LT's that's what stacked AM and RI can do, only one guy had EF and by the time it was down, it would be dead.
That's just what you can do with an all Rad/* team.
