Your use of the term neutralized to me implies that adding more oxalaic acid would slow the speed of that solution. Did you find that to be true?
Sorry, made sense in English but chemically wrong. The oxalic acid sticks to the arm and prevents it from bonding with other molecules. So in that sense it is neutered, neutralized, restrained, whatever you want to call it. But not neutralized in the acid/alkali PH kind of way. Usually the speed will go up because there are more free floating individuals that don't need to be untangled before they can match up with a metal salt. But this has its limitations, eventually some metal salts will start to fall out of solution spontaneously, especially silver nitrate (hence the classic silver nitrate test for free oxalic acid). And I suppose the solution will be even more acidic, rather than neutral, but I'm not 100% sure.

Rudiak and Kennedy only being tested against current (at the time) B&S powder and not against other FO powder on the market.
Yes indeed. There were no other powdered ferric oxalates available at that time.