ORIGINAL: blw
I don't think that outside temperatures have much to do with the glow plug selection. The main problem I think happens is that the hotter plug burns the fuel faster or more efficiently. Otherwise, with something like the OS 8, the crankcase gets loaded up with excess fuel. You can see this happen when starting the engines or letting them idle for long periods like on approach. From what I've seen, you can't tune this out with the needles. Also, I noticed that I had a significant amount of more power when I went from the OS 8 to a hotter plug with my .46NT. There was a big wow factor on the first takeoff.
That is one area I think OS has the edge, their carb are really nice and seem to tune better then most I bet swapping a OS carb on to a trouble maker engine would fix many a complaint about the less expensive engine face it they had to save money somewhere and the carb is the most complex part on the engine to make