Well to be honest I've never torqued a wheel nut in my life. I just use one of those cross-brace wheel nut wrench things and go around and around (well diagonal-ish) until they're all tight and even. Not quite as tight as I can, but pretty damn tight - just so long as I'll be able to get them off on the side of the road with some effort. (No I'm not a huge bloke). I have never seen a mechanic or wheel shop torque a nut either. They use rattle guns that are set to a torque, but a lot over do it and hammer the things on. Not all that accurate. And they certainly don't change the setting for each car, so they're probably set closer to the 125 mark than 170. (or whatever most cars are). I'll check later today if my torque wrench goes that high. If it does I'll try to work out what mine are at, as they were last done "professionally". Doubt it does though. - Ever done a crankshaft pulley bolt? 325Nm on the VN!!! No that didn't get measured - in fact I bent my mates torque wrench (the solid arm with a needle gauge type). I read that as "as tight as you possibly can, use a handle extension on the socket". Not all things need to be torqued to absolute specification.
I don't know how long you've been doing that Adam, but have you ever had a nut feel loose? I'm guessing not. If they've never been loose then I can't see why that's not tight enough. If even 1 has been a bit loose, make them a bit tighter. Personally as long as a) they're even b) you can get them off on the side of the road and c) they aren't coming loose then I'd say that's good enough.
nb- I'm not a mechanic, or ever worked in a tyre shop. Just an opinion of someone who knows no more than you most likely.