Depending on what's already in the conduit, UTP will probably work fine. I would definitely just pull fiber and avoid STP completely if EMF is an issue, or if you're thinking of expanding anything.

5e UTP/STP 100 MHz, 1 Gbps 6 UTP/STP 200 MHz, 10 Gbps (<10 m) 6a UTP/STP 500 MHz, 10 Gbps (>10 m) 7 STP 600 MHz 10 Gbps 7a STP 1000 MHz 40 Gbps (<15 m) The Real Twisted Pair ...