Valvetrain isnt really effected by boost as much as it is effected by rpms. There are lots of people that run stock valvetrain with BT's up to 8000 rpm all the time with 0 issues. Doesnt mean that its safe, I personally wouldnt even think of going big turbo (which I am) with out upgrading the rods and an atleast doing upgraded springs and retainers. Like Caan said 300whp is plenty for a FWD car, but limiting yourself to that number isnt fun. I'd rather be able to turn the boost knob up if I had to and not worry about the motor taking a shit.