Gotcha. You are cooking pretty low, then.
Try this:
Season steak and set on counter for 30min or so. Then put it on a cookie sheet in the oven at 250° or so for about 10 min, until internal temp is 90deg. While it's warming, get that cast iron stupid hot on high, then right as you see 90deg, put it in the skillet for a min or two per side until you see 125-130deg internal.
Super delish.