Good for you! ...both in expanding your remediation efforts outside of the SP3 hardware and reporting back to us on a problem solved.Thanks everyone for your replies. As it turns out, the issue was actually with my router. For some reason it wouldn't allow connections on the 5GHz band. I reflashed the firmware and bingo, now connected to the 5GHz network!
Feel a bit silly now blaming my Surface. Loving it so far.