I just contacted japanparts regarding the red Sti struts and they told me that SG5 and SG9 struts are different. Springs seem to be different too as in the website the red ones are only listed for the SG9 model:
http://www.japanparts.com/db/partslist.php?dealer=1&car=11&middlesmall=3:9&maker=4&volkey=1005G-053-049
This is the answer I got
"Thank you so much for your reply but SG5 and SG9 springs are different. Since your car is SG9, Sti does NOT sell the strut because OEM strut is already pretty good one. "
So it looks like Sti only do springs to be used with the OE struts in the Sti.
Unless they have messed up the website or yuki is not well informed.
Actually, looking at this japanparts.com : PARTS DATABASE it looks like there are no Sti red struts for the SG5 Sti either but only for the Crossport and XT.
http://www.japanparts.com/db/partslist.php?dealer=1&car=11&middlesmall=3:9&maker=4&volkey=1005G-053-049
This is the answer I got
"Thank you so much for your reply but SG5 and SG9 springs are different. Since your car is SG9, Sti does NOT sell the strut because OEM strut is already pretty good one. "
So it looks like Sti only do springs to be used with the OE struts in the Sti.
Unless they have messed up the website or yuki is not well informed.
Actually, looking at this japanparts.com : PARTS DATABASE it looks like there are no Sti red struts for the SG5 Sti either but only for the Crossport and XT.