You have to remember the time frame, yes, you could go well past 7000 rpm, with an FE, but metallurgy was that the valve springs didn't last very long. A good friend of mine raced a 427 Hi-Riser, in a super modified oval track car, if he limited rpms to 6800 max, the valve springs lasted half the season, start turning it above 7000, and you found yourself changing valve springs every 2 weeks. But this wasn't just FE, BBC could last fairly well at 7000 rpm, but move it up to 7300, and you were checking the valve train after every race.
It really is amazing what today's metallurgy, PAC springs can do.