Oil viscosity - why the 20W-50 BS?

Everyone has an opinion. Me, I run Rotella T6 5w-40 and here's a few reasons why.

- I need to run at least a 40w oil to keep hot idle pressure up. A good 10w-30 was only good for ~10 psi hot oil pressure in my engine, and while still ok (1 psi per 1k rpm rule), wasn't high enough to make me comfortable. My engine bay gets HOT.

- I like the lighter viscosity for cold weather start-up. I don't know about you guys, but when my engine starts it shows no oil pressure for a second or so. Running the 5w oil give me a little peace of mind knowing it will get to vital parts a little faster, even if only by fractions of a second.

- Now this isn't necessarily the most important thing, but at $21.36/gal (Walmart), it's a good value for a name brand full synthetic.