If according to the rules, metamagic would bump a spell to beyond level 9, is it usuable? Or basically is it possible to use metamagic with level 9 spells without 3 ranks of Automatic (Still/Silent/Quicken)?

Let me get this straight, just so I understand you correctly:

You want to know if a Maximised Horrid Wilting can be cast in game as a lvl 9 spell? The answer is no.

OR for that matter, you can't cast a stilled lvl 9 spell, no matter what if you dont have the three Autostill feats.

Does that answer your question?