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What do you guys use, and/or, get your safe RPM limits for your motors?

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I try shifting it when it quits pulling hard, I then look at the playback tach and see what RPM that was My 518 C.I. pump gas motor wouldn't quit pulling hard until above 7800 RPM according to the playback tach, I got chicken on that motor and made sure to shift it between 7000 and 7400 RPM It had CAT brand forged steel 6.800 long rods,supposedliy 4340 Chinese forged steel crankshaft at 4.300 stroke with 2.200 rod journals sizes It is still running hard as far as I know, I traded that car off two years ago. The current 505 C.I.motor has a forgd steel Ohio Crankshaft CO 4.25 stroke crank in it with a set of RPM 6.700 long BB Chevy type rods in it, I shift it at 7000 RPM and it has crossed the finish line last year, with 5.86 rear gears (I changed them last winter to 4.56) at or a tiny bit above 7800 RPM, it definetily had its tonque out the last two to three hundred feet in the 1/4 mile Better to be safe than sorry, shift it early so it lives longer