Have u considered Wilkinsons suspension? They did an awesome job of setting up my RX7 that included having to deal with 20" wheels as well Brett has experience with WRX's as well so may be worth dropping in and having a chat.

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"ALLPAWS" 2014 WRX RS 40 - modding very slowly.
2002 Mitsubishi Airtrek Turbo R - Ralliart Edition (daily)
2010 Nissan GT-R - when the Missus let's me drive it :)
Crotch Rockets . . .