Lowering springs for my S4 cab

I want to replace my standard springs for some lowered ones which would make the car sit better with the new 19" speedlines which are on their way (courteousy of N8). Having read previous posts, it would seem H&R springs are my best all round bet, but does anyone know what sort of drop I can expect, as I have read several posts regarding the S line model not achieveing the specified drop as stated by spring manufacturer as that model is already lower by 15-20mm than the standard model, so would mine be the same or is mine lower again than the S line, which would mean I would need a much lower spring to compensate. Just want to drop it 35 to 45 mm but dont know what height springs would help me achieve this.

Anyone help??