Lowering springs for my B7 S4 cab??

Am running a set of 19 x 9 OE BBS Speedlines on standard S4 suspension and wanted to lower it, using H&R spings. Could you supply these?? If so at what cost? Would you recommend any others? Not sure how much lower my car sits than a standard a4 cab, as reading posts on here, the S line sits lower than standard, thus in turn needing larger drop springs to achieve a desired actual drop. if that makes any sense! (ie if you want a 30mm drop you have to buy 50mm springs as the s line sits 20mm lower than standard). Does mine sit at the same height as the S line or lower still?

Thanks