I made the same switch a couple years ago (GMail -> Fastmail) and have had the exact same (pleasant) experience. Fastmail is fast and has sane defaults, a powerful filtering system, and good spam detection. As a bonus, I don't have to worry about Google reading my email to show me relevant ads. I've gladly spent the money to have reliable, fast, standards-friendly email. The only thing they lack is two-step authentication.