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Testing has show for a given intake profile they will give a little more power with a longer exhaust duration.

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Whose testing? I've seen some that show that the proper single-pattern cam will provide more power through the entire range. So, who do you believe?

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The magic number, here, is 75%.

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Sorry, there is NO MAGIC NUMBER. That "75%" rule is outdated.

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Opinions are just that...

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I won't argue that point.

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Well, if opinions are "just that", then I'll consider yours to be the low side of the analogy. You've certainly provided plenty of facts to support your rant, there..... (oh, maybe not) Until you can show me actual numbers that say the 75% rule is untrue, I'm going to consider your opinion completely arbitrary. Perhaps I should have called it a "rule of thumb", not a "magic number", this I'll concede. But the facts remain. This number is based on the physics of volumetric transfer. I don't think these mathematical equations "expire" with time. Why does just about every internal combustion head ever manufactured feature an exhaust valve approx. 75% of the intake? You may really mean to point out that this rule of thumb isn't foolproof every time??. To which I'd still ask you to come up with a fact based equation that outweighs it. Bottom line, heated exhaust gas needs approx. 75% of the volumetric space to travel at the same velocity as the cooler, wetted intake charge. If a heads flow capability doesn't support that mathematical certainty, then adjusting the exhaust valve duration to compensate has become the accepted path that cam manufacturers have followed.