I also ski race and drive a 3er.
I can fit 2 pairs of SG's in the ski sack. A 209cm and a 201cm. A GS and SL ski
(186cm and 165cm) also fit together with their respective poles.
To take more than 2 pairs I take our X3 with a box on the roof or put the box on the 335.
Fortunately, most my skiing takes place at my home hill, so I don't have to move the fleet around that much.
"I know you were offended, but jummo's advice was sound."