It's a very good point this, Pudding.
I'm nowhere near big turbo levels, but as you know I now need an uprated clutch as a result of squeezing more boost out of my little k03. And it got me thinking - what's the next weak link in the chain for me? Being a BWA it'd be rods. But then what? Will I really wake up one day and think "I'm happy with xxxbhp, no more power"? Hmmm.
We can keep uprating parts to cope as we go for more and more power, but as we do that it only makes another component the new weak link, rather than eventually getting to the point where the whole drivetrain and engine is bulletproof. And it comes to a point where driveshafts are failing, or boxes, like you say.
It's hard to know where to draw the line, and when to realise things are getting silly. I think I'll end up sticking to my long term plan of a k03 hybrid at a modest 320ish bhp. Keep the k03 response, stay within the limits of a usable uprated clutch, and hopefully not stress the rods too much.
But anyway, good post mate