Remember OE quote thin winter viscosity because many of their cars have to start in temps as low as -30 degree Centigrade (eg Scandinavia, Poland etc). If your car actually rarely starts in temps much colder than 0 degrees then changing to a thicker viscosity is not such a bad thing. If you car makes a lot of heat (due to tracking/fast road or simply due to big power) then a thicker viscosity is likely better too.
Lastly, IMO rather than discussing which oil is better than another by some tiny amount, the key is to change your oil more regularily. If you push your engine very hard and/or it is highly stressed then a regular oil and filter change is FAR more influential than whether you used Shell/Mobile/Castrol or any other manufacturer. This is because no matter who made the oil, it will 1) Breakdown and 2) Get contaminated with metals, fuel & carbon deposits.
Based on those 3 points above, I myself use a w50 grade oil, and it so happens to be a very cheap one (£15 for 4 Litres) but I change it every 1200 to 1500 miles.
I've got to disagree Nev;
Thinner winter viscosities are used for fuel economy benefits, not starting temperatures, however that means the entire engine is specified around that viscosity. Increasing the winter viscosity can stress the oil pump and lead to oil starvation at startup. Oils can take up to 2 minutes to reach the valve train from start up.
Small brands/ unbranded oils have less value in their brand and regularly blend off-spec oils. Usually these don't use additives as they are more expensive, and can lead to engine failure in minutes. This happens a lot in the US, but is more common than I would like in Europe. Larger brands don't do this as much because the damage to the brand is significant.
Finally, there is a massive performance gap between minimum specification oils and those carrying a lot of manufacturer specifications. With these engines you really do need the extra headroom, as some aspects of engine wear are a linear function of the oil performance rather than 'falling off the cliff' when the oil reaches its end of its life. For example, an oil with poor piston cleanliness will result in the same piston deposits if you change it regularly or infrequently over a set time period.