How great of a difference would there be with typical outdoor CAT5e cable running up to an AP cluster through a quarter-inch thick metal housing, compared to standard STP?

I don’t use any shielded cables. My primary AP tower has a business-band (500MHz) repeater on it, which I was initially concerned about, but I haven’t had any problems. The Cat5 cables travel up the tower in metal conduit, but they’re exposed for the last 20 feet.