Well, technically boost pressure *does* have something to do with it, because on the stock turbo, at a given psi, you'd know that the shaft is spinning at X rpm... so we know that at around 13-14psi, the shaft on a stock r33 turbo would be doing the magic 'breakpoint' of X rpm, and would break itself into teeny bits and pieces.
I'm not following your example... feel free to enlighten me on what 'VE' is... but anyway... I disagree with it.
When the shaft is doing X rpm, it will fall apart, and you can use the fact that the *stock* impeller, will be pushing X PSI at that point. Even if it was spinning up faster or slower, that won't effect the shaft speed at which it'll break. Changing your cams or a manifold or exhaust system won't change the fact that the turbo will break at roughly X rpm, and thusly, will break when the stock impeller is generating 14+psi. Those mods won't change the spool profile of the stock turbo.
Edit: I've actually walked away and thought of something. I apologise, you're dead right: with a bigger intake manifold, tehre's more space for the turbo to fill up, therefore the turbo will be at Breakpoint rpm, but not reached the magic 14psi. Therefore, it will break at a lower psi. However, if the intake/manifold is stock, and the exhaust is changed, or the cams have changed, it won't break at an earlier psi, it'll just reach that psi faster.