PB, I believe that the definitive Lycoming service instruction is number 1014M:
http://http://www.lycoming.com/Portals/0/techpublications/serviceinstructions/SI%201014M%20(05-22-1995)/Lubricating%20Oil%20Recommendations.pdf
The SI recommends 15W50 for all temperatures and my A&P recommends Total Aero DM 15W50, so that's what I use year-round in my MX-7-180. Winter starts are quick and oil pressure immediate. It is readily available all over Europe, although my engine runs almost from one oil change to the next without top up.
I understand the argument in favour of old-style oil for old-type engines but I don't buy it - any more than I would choose to run a Lycosaurus engine without a cartridge oil filter or engine monitor just because it was common practice to do so before WW2.