You'll get about as many different answers to this as there are replies: everyone is an 'expert' on what oil to choose!
LONG ANSWER:
There's a long-running debate about Selenia 20k (10W40) versus Selenia Racing (10W60). The higher (hot) viscosity of the 10W60 is intended to provide more protection under extreme driving, where oil temperatures might conceivably exceed 115 deg.C for extended periods. In reality, such temperatures are hardly ever attained.
The truth is that these engines, like most high capacity motors, contaminate their oil relatively quickly (with combustion products and fuel dilution)so the best thing you can do to preserve your engine is simply to change the oil more frequently: I change mine every 3000 miles, which some will say is 'over the top', but my engine is spotlessly clean internally, runs perfectly, and uses virtually no oil between changes. Strangely, manufacturers tend to specify the same oil change interval on an entire range of cars - from the smallest engined to the largest.
For what it's worth, I use Redline 10W40 which is a fully synthetic polyol ester. These have a higher film strength and much better high temperature stability than polyalphaolefin synthetics like Mobil 1, although both types of oil are fine in road-going cars like ours: Because of the temperatures encountered, F1 engines use polyol esters, and so do the bearings in jet engines! Of course, polyol ester oils are expensive, and ester oil manufacturers say that you shouldn't use these oils for running-in/breaking-in a new engine, because they are
too slippery.
There are many 'synthetic blend' motor oils, and the trouble is you don't always know what you're getting, or how they're formulated. The mineral (i.e. non-synthetic) components of these oils are likely to oxidise at a lower temperature, so synthetic/mineral blends might not necessarily offer better temperature stability, although they probably do have higher lubricity in normal driving conditions.
SHORT ANSWER:
Use a quality synthetic 10W40 oil, and change it often.
But what do I know? Many answers from other experts will follow....
