Leaving the 4V engines out of the discussion since they are clearly high preformance (but at an enormous cost since SVT lost money on every Cobra it sold).
The 4.6SOHC is more advanced than the 5.0 but not necessarilly superior.
Yes, displacement had a lot to do with the LS1/LS6 F-bodies beating the stangs. GM went from 5 to 5.7 liters at the same time that Ford reduced displacment.
I have daily-driven a 4.6-4V, a 5.4-3V, and a 4.6-3V. They are great little (big...LOL) motors although a bit low on torque for their applications. My F150s could REALLY use more grunt and my 97 and 05 Mustangs are both heavy-arsed pigs. But in all honesty I'd rather have the 5.7LS6 in there any day of the week. The LS6 is the only thing GM has made in 30 years that I like.
There is nothing about a OHC that improves breathing per-se. An engine's ability to breathe has more to do with valve size and intake runner/port and combustion chamber design than how close the cam is to the valvestem. Eliminating the pushrod reduces slop and flex thereby increasing efficiency of moving parts, but the additional moving parts (6-foot long timing chains mainly) eliminate much of the reciprocating assembly slop that was saved. I do think it is a similar discussion with the FWD/RWD, eliminating the huge ring and pinion, and the long driveshaft does save a lot of parasitic loss. That is one reason why the typically underpowered commuter cars almost always are FWD, the designers wanted to maximize power and increase mileage. Of course the biggest reason is passenger compartment space but that is even further off-topic
I just think that dollar for dollar you can get as good or better performance from a pushrod motor as you can from a 4.6SOHC, and you don;t have to mutilate the engine compartment and compromise the chassis to fit it in. I know I am a throwback neanderthal, I mean I prefer the sucking sound of a carb over EFI, but this
IS the classic section right? Give me $10K to build (and install into a classic Stang) a 427W and put it up against a 4.6SOHC....that budget would have to include the full
suspension setup too of course...and my money would be on the pushrod version winning the race...be it a drag strip or a road course.