The Flow throughs are indeed a bit restrictive when adding air. I generally just remove them like a valve stem and add air if it's more than a few pounds.
I still like them better than the non flow throughs, as you don't need a tool to remove them.
As far as steel valve stem to fit, use these:
Metal Valve StemsThe bend in the valve allows the sensors to be oriented such that they don't protrude past the edge of the tire.