[Tom Vaught]

Look at it this way:
Naturally aspirated the pressure going into the engine is 14.7 (sea level conditions for this example) psi.
The Pontiac distributor has a vacuum can that adds say 10-12 degrees of additional timing under light load/cruising conditions. So if you have 32 degrees of Initial and Centrifugal timing under a light load cruise condition you could have 40 or 42 degrees of timing in the engine.
(THIS IS JUST AN EXAMPLE OF HOW IGNITION TIMING WORKS)

So you add more load to the engine quickly and two things happen. 1) the load on the engine is higher so the vacuum in the intake manifold drops (dropping the vacuum in the "timing advance vacuum can" on the distributor) and the 42 degrees of total timing goes very quickly back to 32 degrees of timing.
You did not hurt the engine by doing this. It happens thousands of times in a month of driving on the street with a Pontiac stock ignition system.

So now you want to remove 8 degrees of timing at 4500 rpm. 8 degrees of timing removed would make your engine less fuel efficient but happier under the higher load condition with less timing.

Unless you are cruising at 4500 rpm on the highway, not likely, you are in an acceleration mode (higher load) so the reduced timing function is a normal situation under higher engine loads.

The question is "When does it seem the "happiest" under that condition".
8 degrees removed, 4 degrees removed, 10 degrees removed? That takes some tuning time to find out as each engine is different.

Read the plugs, play with the timing, and find out what your engine is happy with for the fuel you are using vs the way the engine is built.

JMT (Just my Thoughts on the subject)

Tom V.