Question for the more knowledgeable folks....
The "Crate Engine" seems to have a redline over 7k RPM. Is the low redline on the other motors more a function of camshaft or intake limitations or other details? I'm sometimes surprised at the lack of "Cam Only" setups, with the exception of a few guys doing a CC cam. My other all motor cars have always benefited from a cam, but of course if the intake and heads won't flow more air then it won't benefit.
The crate engine surely has a strengthened bottom end, and also appears to be running a revised valvetrain, probably a solid roller setup.
However, your question is rather complicated actually. Generally speaking with regard to the two Gen-4 based setups in this thread, the lower redline on the other setups is mainly due to the valvetrain. The Gen-4 based valvetrain, while MUCH better than any previous generation, was designed to be a long-life street based valvetrain revving to 6500RPM or less. As you increase RPM, spring pressures need to increase, lifters will eventually need to be solid because of this, etc, etc. The end result is a shorter life higher maintenance valvetrain. No problem for a Drag engine, but not the best for a street engine.
However, thats not the whole story. The Drag engine is Gen-4 based, the G4 conversion engine is Gen-3 based. Gen-3 Oil Systems are not very good in those higher RPM ranges. The Gen-4 oil system however, was designed from the start for higher RPM applications, as the Gen-4 power band was shifted up. That is the primary root cause.
Now that being said.... with the right combination, all of the above goes out the window.