Needing notes

Whilst I’m thinking about all these different topics that I’m interested in, can anyone help? I’m in the market for a new desktop note-taking tool. It must start up in <3 seconds and save each note as a standalone text file, using some form of text-based notation (like wiki, textile or markdown).

If that didn’t eliminate enough options straight away, it would ideally auto-save every few seconds and allow tree-based note hierarchy. A couple of tools have come close over the years, such as WikidPad, Zim and KeepNote, but none have quite hit that sweet spot.

So, any suggestions? I am willing to pay!