Stilson, I would stick with OEM 1.447 LR unless you want to go to 1.59. Then the ADS one will fit in with a 4.111 crown wheel with NO mods or the 4.44 with minor machining. It will also be stronger as Catchya said.
For Catchya, you might benefit from the stronger LR with your increased torque. Just remember, its still vulnerable so change into HR whenever you can & don't dump power through it.
I'm not sure the OEM gears are cast, pretty sure they're machined just not as high a grade of steel as ADS uses
SG 5th is .780 in AUSAlso, I was reading something on SF.org about using an L-series 5th gear as it's longer than the Forester's, is this possible? If so, then I could just buy an L-series DR gearbox, STi RA DCCD 4.44 LSD box and modify them both into my SG box and have everything I want (apart from the ARB locking R180 rear)...