The right Subaru trans will handle up to 450hp on the "street".
Adapters for offsetting the shift rod to output can be made or purchased for VW applications, so I imagine the same for 911 apps.
After flipping the R&P, converting to 2wd via SubaGears kit it will be able to handle 3.6. The WRX puts out similar or more power/torque depending on model & origin. JDM is more balls.
A full Subaru STI swap would be sweet in a 911 for many reasons other than resale.
There is no kit for the six speed, yet.... but that may be remedied by the time you finish this sentence.
The Subaru 6cyl 3.0R has big potential.
We have recently installed a JDM WRX engine/trans into this 62 Kafer. Lots of cutting, some welding and swearing but it's going together nicely. This one is 260hp/260trq in factory trim. After the transplant and mild mods it should be knocking on 300hp's door. This is a 1675# Street Bug. Should be interesting. ;-)