(assuming stock Subaru Sways are made of the same material....)
Isn't the stock STi front bar 22mm??
so the WL 29mm bar would be: 202% stiffer... where as the 27mm would be 127% stiffer, close to the Swifts 122% increase..
I guess to make some HUGH ASSUMPTIONS... the swift set-up would be "similar" to a WL 27 FSB
may help answer some of your questions.
I am curious about pricing as well as whether these SWIFT bars include endlinks, bushings, mounts etc...