FSkillUseMajorMult

Modifies the number of times you need to use one of your 7 major skills in order to get a skill increase. The base number of uses depends on the level of the skill and other (unknown) factors.

In the default game this value is 0.75, which means your major skills increase 25% faster than average. However, there are no 'average' skills: the increase of minor skills is affected by FSkillUseMinorMult and the default value of that setting is 1.25, which means that major skills increase 67% faster than minor skills.