Just placed my order for ds2500 pads with the group buy and asked the chap about discs as I was thinking of going black diamond grooved route, he said he could get pagid fast road discs with 8/16 grooves. Has any one got any experience of these or shall I be the Briskoda test pilot for this set up ?

Not of those discs but have had both 8 and 20 groove discs before on another car.

I'd be tempted to go for the 8 grooves over the 16. Move grooves just reduces the surface area of the disc.