I have a python script that runs nightly via a .cmd file which takes a feature class in British National Grid (BNG) from one database, adds some fields and then calcs lat/long decimal in WGS84, X/Y in BNG and converts the lat/long decimal to text. Everything works fast apart from the lat/long decimal in WGS84. Its approx. 60k records, Approx. 40minutes for the full script but 35minutes for the lat/long decimal in WGS84. I'm not an expert coder and just managed to google enough to have this working.