IMHO I have used both steel cast cranks over 7000 RPM and as long as either I'd prepped properly both are good castings. It is more the application that determines what crank is better. I would not use a cast iron crank for a high performance engine for example, it will not last.
Sorry, gotta call BS on that last statement. I have ran nothing but factory Ford 428 cast cranks in my Fairmont for over 20 years with no failures. I have used the same, 45 year old 1U 428 crank in 3 different 428s in the last 14 years, one block split the main bearing webbing, one split 2 cylinder walls, and the 3rd kicked out a rod thru the block, but the crank is still good, and waiting for another build. Also the 454 cube 427 currently in the Fairmont also has a plain old 428 cast crank in it, as does DalePs 9.7 ET 67 Mustang. Dales crank has also been in there for many years.
As for Eagle stuff, I know a few FE racers who have had Eagle rods break. As much as I hate to admit it, the 331 cube SB Ford in my 85 Mustang has an Eagle crank and rods. The first crank ate up its thrust surface after 2 years, opening the thrust clearance to .050"! So far the 2nd crank seems to be OK. I`ve never had any thrust wear issues with any of my factory Amercan made Ford cranks. Although he always uses Crower rods in his own Chevy race engines, my engine machinest does use a lot of Scat stuff for customers with tighter budgets. He says the Scat stuff is fairly decent, but he doesn`t care a lot for Eagle or RPM stuff.
