you should not powershift in any transmission. people have this impression that the sti transmission was built by god himself or something. abuse an sti trans and it will break just like every other trans in existence. is it tougher than the 5 speed. sure. is it invincible? hell no, powershift and launch an sti all the time and itll eventually break.
google PPG gears if your concerned about your 5 speed and want it stronger