As has been touched on, it doesn't matter which end of the grooves or drilled line you have leading, they'll both perform in the same way but, shift the crap in a different direction ! Personally, I like to have the drill hole nearst the outside of the disc leading, as on most OE drilled brake systems.
As geetee has said above, the function of the grooves and drill holes is to shift the gas byproduct away from the pad/disc face to reduce/eliminate brake fade. An added function of a grooved disc is that it can also deglaze a pad face as, it basically skims the surface of the pad when the brakes are applied, on each disc revolution.
And neither method is for disc/pad cooling, that's what venting the disc achieves !
Personally, if you're just using the car on the road, I'd go for a high quality drilled only disc as, it'll help the pads to last longer and be much less noisy with less vibration in operation. Drilled discs are also self cleaning where as grooved tend not to be as good in that area so, negating the function of the grooves.
I say a high quality drilled disc as, if the casting is not up to scratch, it can crack around the drill holes.
If you use a good high temperature pad, you shouldn't have to worry about the pad glazing either !
thats what i was thinking it would far eat pads the other way, i think someone put the sticker on just to confuse matters:?
