Re: Regular screws vs Allen screws vs Rails?
Rails allow you to bend a note and the string will always be over a polepiece as the whole rail is the polepiece...so there's no drop off at all. The drawback is that you can't adjust a rail up or down under the B string if that string seems out of balance with the other strings, as it usually does. As for the diff between slot head screws and allen screws: I think there is a tonal diff, but I'm not sure how to describe it. Maybe the field is a little more dispersed with the allen screws? The tone seems a little less focused, less steely and more spread out with the allen screws. The harmonics seem to have a little more space to thier tone with the allen screws. But I could be wrong about that as I've never had two identical pickups to compare with one having slot head polepieces and one having allen screws.
Lew