FWIW, add my vote to the "follow the manual" category--although there's still latitude there. My 560SL manual specifically confines 10W-30 to ambient temps under 50F. Preferred options for 32F up to over 86F, which covers my driving season here in Michigan, are 20W-40, 20W-50 or SAE30. What I've started running is 20W-50 formulated for high-mileage engines, which describes me at 146K. The 10W-30 that somehow got in there at the last change (NOT my idea!) definitely wasn't the ticket for stop-and-go traffic at 70F ambient; loading up with blue smoke from rest, not noted since the change. Guess it's another vote for RTFM.
'97 SL500, 40th anniversary edition
'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)
SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)