I've been using whatever 5w-20 I've found on sale in my girls windstar for a few years now. It's got over 320k on the odo as of right now and consumes nothing between intervals.
I'm also running the filter for 2 oci if it matters to anyone.
Thru the fill cap the head looks very clean without any varnish or deposits.
As far as oil choice in a mod motor from experience I can tell you thicker affects the free rev ability of the engine and that's about it. They will run forever regardless of grade used.
In the mods I've owned and maintained I've seen firsthand 2v 5.4 trucks with in excess of 400k on the odo,work trucks used as such,that ran 5w-20 their entire lives and they are still running and getting beat on daily.
The mod motor is at least as durable as the Windsor it replaced and tolerant of pretty much any grade you choose to use in the sump. Using a heavier grade will not affect longevity whatsoever and should only be considered if used in a heavy duty fashion where oil temps will be elevated well in excess of "normal".
My friend has a 2001 f-150 with 350k on the odo. It's the fully loaded variety he bought new.
He tows his trailer with 4000 pounds of stucco equipment daily,to and from work and chances are he's got sand in the box with the trailer attached.
He's had it since new,he's operated it in the manner since new,used 5w-20 conventional in it at 5000 mile intervals since new and with the exception of brakes,tires and oil changes has done nothing else in regards to maintenance.
If ever I saw a 1/2 being run to the very limit this truck is it yet unhook the trailer and clean it out and it looks,and runs as good as new.
So my personal experience has proven to me that going thicker is pointless unless there is some reason to do so. A mod motor just doesn't notice or care.