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So keep in mind a 0w40 is not the same as 40w. I have also found 0w40 to be a poor oil at high temps and it has a lot to do with the large viscosity spread. Polymers are added to the oils to get this large spread and it makes the oil less stable at higher temps contrary to the advertised viscosity. A 10w30 actually works much better than a 0w40 from my testing.
Last but not least don't expect the world from your oil's rated viscosity as once hot, you will be lucky to get +5-10 psi which is why it was so critical I added a Perrin Oil Cooler kit to our car. So the actual viscosity of the 50w race oil I run may only be a 30w at 260F. Now I know 50w sounds scary to some but Red Line race 50 actually has a 15w50 rating but it just stays in grade so much better than most oils at suoer high temps.
Don't be affraid to to go up in viscosity to test yourself as I can tell you with absolute certainty there are no clearances in your motor that should freak you out. If you need to daily drive in freezing temps 10w30 is probably the highest you want to go for boosted cars but in the summer I've needed everything a 50w can give me. NA guys should probably stick to 0w20 or 5w30 for winter use.
For what it's worth our race car runs 50w Red Line Race even in 30 degree temps. Even with a mini battery, dry sump, Hydra EMS stand-alone, big valve heads, and 280 cams, it starts right up and that says alot about how well that oil flows (non synthetic or even blends at the same viscosity are extremely hard to start by comparison).
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