Well they say the less points of friction the strings sits on the better it will stay in tune, and that is what happens on my MIM mostly not so on my highway one because the highway one's string trees are different they are like pins and there is less contact with the strings in theory............

The string trees with the "pins" you described Synchronized, are the Ezy Glider String trees. Those are the ones I've put on my 57' RI with the Gotoh vintage style locking tuners. These work great with the particular set of locking tuners I have since the posts of these tuners are the same height. I've found that if you use the staggered post tuners such as the Sperzels, it might be better to remove the string trees since they do pull the string back and downward from the nut.
As for the old style string trees, they don't really work that well. Too much surface area contact on the strings. They are very difficult to keep a guitar in tune if you use the tremolo.

There's my .02 cents, FWIW

-Harley

_________________
I only have two brain cells left, and I'm saving them....for this weekend!