IIRC, the only difference between HD and SP is that SP is for short springs. I LOVE my SP/Eibach (VW Eurosport) suspension in MkIV Variant. Yes, considerably stiffer than the stock US market mush-crap, but this is my wife's car and even she vastly prefers the handling and feel with the SPs and higher rate Eibach VR6 springs.