Re: WHY 300k pots in les paul studios?
300K pots have been standard in Gibsons for years. As far as what pot is best, it relates more to a pickup's position than anything else. String vibration & power makes the two locations totally different animals.
A 300K takes off some treble, so it is excellent for a bridge PU, but not so good for a neck, as it darkens it further.
Likewise, a 500K brightens a neck PU nicely, but makes the bridge much brighter, which it usually doesn't need.
Manufacturers keep their production line & inventories simple by carrying one pot value, but one size does not fit all. Using one pot value for both bridge & neck helps one PU & works against the other. This is true for LP's and any other guitar. Using 300K (or 250K) on the bridge PU with 500K on the neck, prevents them from being complete opposites tonally, & therefore MUCH easier to get a good amp EQ setting for both. Otherwise you dial in one PU & the other is usually way off and rarely gets used. Just like you use different pickups for bridge & neck, you should also give some serious thought to using different pots for them too. Why copy the manufacturer who's only trying to keep his costs down?