There is LOTS of info on the Subaru 5 MT tranny online. Most guys will agree that it's safe to about 350 HP, even with hard launches and occasional track use. 6 speed is more robust, but is slightly larger also, with its built-in oil pump. PPG and Subarugears each make r&r kits to beef the 5-speed up, with escalating costs to match. Every source includes a caveat that no amount of toughening makes the tranny idiot-proof. I quit serious shopping when I read that.