Guys just to clarify on what the oil symbols mean.
As far as i'm aware (I stand to be corrected if someone else tells me otherwise), both symbols relate to oil thinkness:
The first relates to how thick the oil is while COLD. The second relates to how thick an oil is while HOT.
During winter, oil is more viscous - its thicker because it's colder. Hence, you're better using an oil with a lower rating to help it circulate around the engine faster.
EG, lets say someone uses 10w40 oil on a standard car (a corsa or something similar). You might want to use 5w30 or 5w40 in the winter.
In my car (Z), i'm currently using 5W40. I would not recommend anyone use more than 5W (cold oil temp viscosity) in our cars as it may be too thick. Use 0W or 5W instead.
As for the HOT oil viscosity, use either 30 or 40. Anything more will possibly be too thick, and will also reduce performance & MPG a little as the friction is increased.
I'll probably use 0W30 in winter, and 5w40 in summer.
Hope that helps!