I just want to point out this nice post from BX BLACKRAZOR about the calculation of experience based on prime requisite scores. Which is based on another post on GROGNARDIA.
Even in the Moldvey/Cook BX, they interpreted it as having to lower other ability scores to increase the prime requisite score.
Certainly one way of doing it, but a possible incorrect interpretation. Here is how a commenter put it for OD&D:
Under Strength:
"For each 3 full points of strength above 9, clerics may consider their prime requisite (Wisdom) 1 higher for the purpose of gaining experience."
Under Intelligence:
"For each 2 full points of intelligence above 9, fighters, clerics, and thieves may consider their prime requisite (strength, wisdom, and dexterity, respectively) 1 higher for the purpose of gaining experience."
Under Wisdom:
"For each 3 full points of wisdom above 9 for fighters, 2 full points for magic-users, or 1 point for thieves, they may consider their respective prime requisites 1 higher for the purpose of gaining experience."In short, In OD&D, high scores in OTHER ability scores could be used to "increase" your prime requisite when determining XP bonus. But because it is written in come convoluted Gygax it is hard to understand.
I've seen a variation of this in the '74 OD&D clone DELVING DEEPER which I also think makes a nice addition to how one can interpret WISDOM in BX:
Wisdom is intuition, common sense, and maturity. Each 2 points of wisdom beyond 10 will add 1 point to the character’s prime requisite for the purpose of calculating experience points earned. Wisdom is the prime requisite for clerics and functions as does intelligence in determining what course of action a non-player character should take.
HOW DOES IT WORK?
Well lets say you roll a STR 15, WIS 12, INT 14. Because your STR is the highest score a fighter would be a logical course. But since your WIS 3 point over 9, you get a +1 to prime requisite for the determination of the XP bonus. And because your INT is 5 over 9, you get a +2 to prime requisite for the determination of the XP bonus.
In total this fighter's prime requisite is 15 +1 +2 or 18! Earning I believe a 20% XP bonus.