well, I could remove my 'faith based statement' regarding viscosity and counter with a list of Porsche-approved oils which has a lot of 5w40 in it:
Porsche-Approved Oils
but, if we take the self-published blog approach (the one that starts with three pages of credentials and brings the statement "methinks thou doest protest too much" to mind) then viscosity is moot, replaced only with wear performance. I can't help but think that this analysis is more geared towards tappet and solid lifter engines, however (ie, should I worry about cam lobe wear or keeping my hydraulic lifters from gumming up?)? similarly foaming - as much of an issue with our 9 litre capacity integrated dry sump engine as it is with a 6 litre capacity wet sump American lump (m96 starvation issues more associated with oil pickup location, sump baffle design and banked high-speed corners?)? in the end I really know nothing about oil; I base my decisions on availability, change my oil every 5k miles and check my filter after every track weekend.
regarding some of the other posts in this thread; only a fool would use olive oil in their engine; that is to be used in transmissions only.