Euro startup sounding like a diesel engine

[JohnL]

you said it right there yourself, with a weaker spring on a very tight clearance, the spring may not have enough pressure to push the valve all the way home...

Then is that a problem with low spring stiffness or with inadequate spring pre-load. I'd suggest it's an issue with preload and the spring needs to either be longer or shimmed at it's base (so long as you could shim it without risking coil bind).

I'm all for using the weakest springs reasonably possible for the red-line the engine sees (+ a bit for safety), stiffer springs use power and cause greater cam wear etc.

It seems to me that so long as any clearance exists then the spring will be pushing (or pulling) the valve shut just as hard no matter what the clearance might be.