Herb Adams in his book "chassis engineering" states that one pound of rotating mass is worth roughly 6 (or maybe it was 8? don't have the book handy) pounds of static weight. I remember years ago switching my car from Magnum 500 wheels that weighed about 26 pounds a piece to weld wheels that weighed about 10, the car lost 64 pounds of static weight but the COMBINATION of dynamic AND static weight reduction dropped the et close to 2 10th's. I was amazed and the car pulled faster through the gears (although the rotational reduction really only applied to the rear wheels) Using 1 for 8 that would mean a 12.5 pound reduction of crank weight (or suppose any rotational weight) would be worth about 100 pounds of static weight or a rule of thumb 10th.

The thing to remember is the crank can only accelerate as fast as the sum total of the rotational forces will allow, The cranks rotational mass is added to that of the tranny, the driveshaft, the ring gear and the axles and \most importantly the tiresagainst the ground so although you are dynamically lightening the crank and reducing the total mass of the drivetrain, it's not just the crank itself and when the totals are summed the percentage weight loss % is (quite) a bit lower than you'd see just revving the motor in neutral.

Also there is a flywheel effect to rotating mass as far as how it Hits the tires at the moment where static energy becomes kinetic. Like a lighter or heavier flywheel there is a trade off that is beneficial in most cases but not necessarily in all cases. I went with a heavy steel flywheelin my 427 CObra because although I'm sure it would accelerate quicker in the 1/4 mile with lighter mass, I wanted the proper big block "feel" when I dumped the clutch as low engine speeds and to offset the very light 1850 gram bobweight of the smallblock. To transfer equal inertia with lighter rotating mass you have to tranfer the load at a higher RPM which is usually an advantage for drag racing. But EVERYTHING is a trade-off, the big slicks you need to launch off the line take a lot more power to turn at the top end, so racing is always a matter of where and when to apply power
most effectively.
also I believe when comparing cranks the effective weight of the rotating mass is the sum of the crank plus the rotational weight of the pistons and rods. you have 2 cranks one weighs 50 and the other 60 it is 20% lighter, but if you included ONLY the rotating (big end) weight of 8 rods (lets say the same 10 pounds) the effective rotational difference is really 60 vs 70 or a net of 16.6% lighter.....now add the sum of everything elese that spins inthe drivetrain.

Interesting topic for sure!