i suppose if you drive a car like a tool anything can be broken. there's no doubt the increase in torque will increase the strain on a stock 5 speed transmission. any transmission when babied will less likely see severe damage. i've seen some damn good drivers and easy drivers alike break lose 1st most often in ej205's and 3rd in ej255's(i'm sure you know all the final drive hearsay that goes around). as it stands, subaru does not warranty any transmission, even if you blow your transmission in stock form, as the majority of the clients we get are still stock.
I'm running on my stock tranmission on my daily beater for almost 3 years now. over 70k on the clock and only 3 monthes after purchasing it new it was putting out 366/411. now with E85 it's running 402/477. still on the stock tranmission.
to make things a little more complicated you may think about doing a V7 ej207 swap. i know finances are an issue but i was able to get mine for $1000 direct from japan. i would not mind putting you in contact with this company if you wish. send me a pm.