I did a little testing a couple weeks ago. I experimented with putting various 5 & 10W30 oils in the freezer (0*F - according to the fridge's LCD).
5W30:
Havoline, Shell, GTX, Supertech(XOM), Valvoline AC; all poured close to the same, which was like a 80W90 weight gear oil.
10W30:
Supertech, GTX, Superflo, Havoline, Maxlife; The Maxlife poured the best, similar to a 5W30. The rest were pretty close, almost like honey.
15W40:
Chevron Delo 400. The BIG surprise! When I conducted each test, I put the oil in the freezer at night (10-11pm) and tested them after getting home from work the next day, about 6pm. When I poured the Delo, I was surprised that it actually flowed. I would say it poured similar to a 10W30. I attribute this to the Isosyn basestocks it's made from, which Chevron claims to rival synthetics. It has a pour point of -23*F. The Delo SAE30 I use in summer has a PP of -24*F. That will be my next test.
This was in no way a scientific test, just something to mess around with. All testing was observed with the naked eye.