On the server I have sogo running so I also use iCal and the Mac and iOS contacts apps.
Search is single-digit ms. All metadata stored on the client.
I built this over the course of a year, literally driven by my frustration with Apple Mail. Maybe give it a try!
Edit: Also, extremely brave of you to upgrade to Tahoe. No chance for me
> All metadata stored on the client.
Passwords, tokens, and attachments stored on your servers according to your privacy policy. And headers, message bodies, drafts, contacts, and flags if encrypted server cache meant what it sounded like. And telemetry with no choice mentioned.