My comments are assuming a late model (1999+) STOCK street driven 4.6 designed for 5W20 oil. Purpose built engines should use the oil recommended by your builder/manufacturer. Anything driven in a race application will have it's own set of requirements and adjustments should be made accordingly.
I suspect this is going to ignite a firestorm (torque wrench), but……..
Ford has designed the late model modular motors to run on 5W20 weight oil. The bearing clearances have been reduced in an effort to reduce internal friction losses (better mileage). As a result, thinner oil is needed to fully penetrate the bearings. The thinner oil is also needed to maintain adequate oil pressure in the top end (hydraulic lifters).
The bearing clearances change as the motor heats up. When cold, the clearances are very tight in locations with dis-similar metals. As the motor warms, the clearances open up. The thinner oil better protects these parts during warm up.
If you need an expert opinion on this, try reading Sean Hyland's book.
Amazon.com: How To Build Max-Performance 4.6-Liter Ford Engines (Cartech) (9781932494686): Sean Hyland: Books
It is also interesting the part about
NEVER getting on your motor until it is warm/hot.
With regards to the noise on start up, it is a very common problem. Ford has a TSB on it. The noise comes from the timing chains. The noise goes away when the oil pressure comes up in the timing chain adjusters.
If the noise goes away within a few seconds after start up, it is a normal noise. You may find the noise takes a little longer to quiet down if the car is not driven every day. If driven every day, it may not make any noise at all.
Note, there are differences within the model years because Ford changed the design of the adjusters. The problem is more common in later model engines using the adjusters that do not "latch" as tight. The older adjusters have a prawl that holds the position without oil pressure.
For high mileage engines, be mindful that excessive wear on the timing chain tensioners can cause noise. If allowed to continue and wears past the plastic down to the metal, failure will result. Inspect the oil filter. Look for bits of plastic. If found, be concerned.
Ford has redesigned the adjusters/tensioners to reduce the noise. Recommend getting the lastest part should maintenance be done.
However, it is not a bad idea to use a premium oil filer. There really is a difference. I purchased an oil filter cutter. I was surprised to see how poorly constructed Fram oil filters really are. The difference is in the filter material and the drain back valve.
In all seriousness, this is an excellent POST! 
but, the older the car, the heavier weight of oil would be neccesary, parts do wear down. With that been said, cars have personalities like people, thats why we get lemons and others get great cars, you just have to know thy car. Can you honestly say that out over, lets say, 10,000 mustangs, every car is going to react the same to the same brand, the same weight, and so on and so fourth. What we have hear is a clone of the FORD/CHEVY debate, its "Beating a dead horse."
