The 06-07 WRX have 3.7:1 FD ratio. You need 3.9.
However the VC in the pre 08 WRX r160s really aren't for performance but for inclement weather driving. VCs transfer torque based on speed differential and are very slow to do so in addition to the fact that the VCs in the r160s are weak anyway.
What sort of driving do you intend to do? Autocross? Track? Why are you so concerned about having 2 tires off the ground?