I had a 2008 WRX that I leased. I put 24k mi on it with Cobb stage II. I took it to several track days, shifted it regularly at 6000+rpm into 2nd and 3rd gear and never had a single issue with it.
90% of the broken 5spd gearboxes around here are driver based. I broke the gearbox in my 2000 2.5RS with a blistering 200chp in the car. I repeat, I broke the gearbox. The gearbox didn't just break.