Any technical guys have any comment on what velocity difference to expect with changes in bearing surface length between bullets of equal weight and diameter, ex. 55 gr. V-Max vs. Blitzking, etc., etc.

Usually, anything that increases the bullet starting force will produce some increase in muzzle velocity by raising the pressure early in the powder burn and causing it to burn a little quicker (also boosting the peak pressure.) It'd be tricky to predict the effect of a change in bearing length quantitatively, particularly as there might also be other differences such as jacket thickness and hardness, core hardness, etc., and seating depth will also enter into it.

The best description I've come across is the article by Waite in the June, 1955 American Rifleman. Your local library should be able to get you a photocopy. The results are summarized in an article by William Davis in the NRA's book on reloading called Handloading, sadly out of print but still available from used book sellers; I got mine via ABE.

Bullet substitution can have a big effect on pressure.

ASDF-- what is ABE??