906 or 452 which is best overall

I believe there is more variance from casting to casting than casting number to casting # when talking these heads.
I have no bench to prove this. Old school aproach kind of opinion here. I do know some carving under the seat and a back cut valve has always been what woke up a iron head big block for me. More so than a simple casting # swap. I dont believe you would feel a gain without this extra effort. I never put a stock head on anything that I have plans of running at even a slightly higher rpm. It doesn't take a max effort thousand hours of testing on a port to get real and noticable gains. Some quick cutting in the most restrictive areas and I have been just as satisfied as when I spent a stupid amount of time on them making them look pretty like seen in the head porting tutorials. Waisted effort in my experience but I'm no pro.
I have broke thru to water after running a few thermo cycles before so you do have to be careful in a couple spots. This is why I have my opinion about casting to casting. Some have more room for porting than others of the same casting #. This luck of the draw can be very disappointing. Pull the head and start over with another.
Depending on the piston I usually will start with a 906 or 915 just because they are considered the muscle car heads.
I think that it doesn't really matter the casting # as they all have plenty of potential and it never make sense to bolt any of them on without taking advantage of this nearly cost free
horsepower even on a stock rebuild. That's my take on these iron castings. Unless your engine needs the max wedge port size or the weight loss of an aluminum casting they
can get the job done very well. My first set I built back in 79 or 80 was a eye opener for me even with the stock valves.