Bilstein has both B4 and B6 options for Gen 5 Outbacks. I have the B4 in front with stock springs and a 24 mm Whiteline sway bar, and B6 in the back with Rallitek non-lowering springs and a 22 mm Whiteline sway bar. I have several other mods and the whole package works well: Continental 245/50ZR19 Extreme Contact DWS tires on Enkei 19" Raijin wheels, and a non-standard alignment (0 toe and -0.5 deg camber at all four corners - Moog adjustable front and lower control arms needed in back).