There is little doubt synthetic oil lubricates better in the low temperatures. How much is the question.
It is very difficult to find the spec's on Permatran published. When you do, you see less difference in the low temperature viscosity then you would expect, when comparing it to the synthetic oil. Permatran really is a very good oil.
Unfortunately, any change in warm up time is speculative.
I prefer to think of the synthetic oil as an insurance policy for that day when your buried in snow, and you just don't have all of 30 minutes to wait for it to warm up.
Or, for when you in the middle of a project, and you hit the oil change interval. With the synthetic, you can go well past any published time, and not worry.
I do reduce my warm up times by about half. But, I keep a 140 watt silicone pad heater, on the bottom of the axle, plugged in during periods of impending snow fall. It keeps the oil from getting very cold to start with. That really does make a difference.