For fire farms, it's still cap Fire Def and Resist. My first run through post changes sucked since I was rusty as I hadn't played in a while, but the second run was clean, and is as long as I don't brain fart my run.
But seriously, there's no real advantage to running +4/x8 in AE versus standard missions. Any decent Stone, Rad, or Bio Brute or Tank is going to run all over Murdertown for regular content for farmable maps. Hell, my Ice/stone Brute did a +4/x8 Council map even before hitting 50, and no, I didn't need Ice Patch. It was slow as watching paint dry though, but it's different now with Incarnates.