They were fighting because with the roosts removed, they have to re-establish pecking order. I would have left the perches in place; if you haven't done so already, please put them back. The air will be warmer at elevation anyway, than on the floor. If you're worried about their feet on the perches, see if you can use 2x4's but turned so the wide side is up. Chickens don't grip with their feet anyway, and a wider space to sit on will keep their feet warm.
I'm glad to hear you switched to a red bulb - that's likely 250 watts, versus the clear one you had that was only 125 watts. The 125 would have done nothing to heat the coop in that extreme cold, it's just a bright light, that's all. The 250 will do better.