There're many parts that can fail to high boost. The open deck is not one of them. Instead it's the last thing to worry about with just any platform. N54 is making north of 1000 and the deck is fine. With N55, I'll say (or conclude) that the turbo is by far the weakest point (that can cause a major fail).
N55 has so limited turbo options because of 1) hot half and manifold in one piece design, and 2) a bottom mounted turbo layout.
There is no hybrid turbo that makes power and runs reliably at above 20psi (middle and upper range). Doing so in long term you're pretty much committed to killing your turbine with the ridiculously high exhaust manifold pressure and EGT. And that's even for the best scenario assuming everything else is done right.
As a good example, one of my n55 buddy just broke his turbine, after 35000km (22k miles) on PS2. There was a short length of time years ago he's running 22psi on meth. But most of time, just logging different pump gas maps from 14-18psi. Other times, used a daily commuter.
He's one of luckier ones, because of his rich tuning knowledge of this platform and 'did everything else right'.
Every platform sees its limit one way or another but people believe what they want and push beyond it. In N55's case, especially with the M2, the limitation is just much closer to stock power than many think.
That being said, everyone has different criteria and priorities, in the end, whatever makes the owner happy matters.
I'll participate OP's questionnaire, but have only one thing to say - Seeing 430whp with STG2 hybrid on pump gas, I already think it's too much power for a N55.
Pardon my broken English
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