Well, the screw polepieces are a little closer to the strings than the slug polepieces, because they're sticking out through the top of the cover, so the screw coil is probably a little "louder" than the slug coil. Because of that, the pickup will probably sound brighter with the screws facing the bridge, and darker/warmer with the screws facing away from the bridge. But it'll be a very subtle difference.
There's another factor which will affect this - most BKP humbuckers have an asymmetrical wind, with one coil wound a little hotter than the other so they "hear" different frequencies. So again, turning the pickup round will affect the sound slightly.
You could just experiment and see if there's much difference, and which you prefer.