Well, things look like they will be moving along faster than expected with the mods - I have managed to secure a set of 135i Brembo calipers (6 piston fronts / 2 piston rears)
Just need to order the BMWP drilled / slotted front & rear discs and then I'll get them fitted! Although they are coming in at £475 from the dealers, so may have to consider aftermarket??