I updated the link.

As engines wear the manufacturers specified oil no longer provide the correct level of protection. Thicker oil simply raises the oil pressure. The uk is a mild climate so thicker cold oil isn't a problem, but it will provide better cold engine protection. Old engine additives are best avoided as they usually work by thickening the oil and softening oil seals (this setting you up for an engine rebuild).

Engines don't all wear at the same rate, even if they're the same type of engine. This prevents manufacturers from stating that at a specific age you should switch to a different oil specification, and without being a conspiracy theorist manufacturers don't want an engine/vehicle to last forever, 10 years is the what is considered a RRS's lifetime. Blindly following the manufacturers guidelines is fine for a new car, but older vehicles require extra tlc so by sticking to the guide book you're not doing what's best for your vehicle.
An example of this the oil in the gearbox and supercharger (for those that have them) the manufacturer states that the oil is good for the lifetime of the vehicle. I'm guessing (the same as most people on this forum that) you didn't have a problem going against what the manual states there ?

There are many other examples where what the manufacturer states is right isn't always best, I'm not looking to argue, but rather than simply shooting people down its far more constructive to provide a counter argument. I stated what gains I would be hoping to achieve quite clearly along with my reasoning behind it.

0w oil may flow quicker but it doesn't provide enough protection to a worn engine, it's oil pressure that you need and being as the oil is pressure fed round the engine the difference between the 0w and the 10w reaching the top of the engine would be marginal, however the higher viscosity of the 10w oil will provide better protection. The 0w oil being thinner would lower oil pressure due to it being able to easily flow out of the worn bearings etc. The higher viscosity of the 10w will raise the oil pressure back towards what the engine had when it was first built.

The flow rate between the 0w and the 10w isn't particularly high, and being as I'm U.K. I don't really need to worry about the winter viscosity.

0w40 will provide no more protection than the 10w40 once it reaches temperature, that's what the second figure relates to.

Tim in Scotland wrote:

I'm no mechanic but I was always told to drain oil through the sump. You get all the particles that may be on the magnetic sump plug out and you can leave it overnight to drip out as much old oil as possible. Vacuum pumps are for service bays where time is money............... and they don't get all the crap out from the sump.