I started on Grade 4 leves at 25 and intend to move to Grade 5 leves when I ding 35.

As for the 30-34 range, I've just been zoning out watching a movie. Thankfully once you're familiar with a region and it's sweetspots, it doesn't require much focus.

From what I can tell, the 5s is the earliest the next Grade's leves are available, which circumvents the need for Arbor Call/Triangulate.