Point of vocabulary: The OP questions about burr size stem from concerns about grind retention. That term will help understand when that is or is not a concern, and also in learning about each grinder's typical behavior. Burr size and single dosing relate to, but are not synonymous with retention. Grind retention also has several qualifiers according to how it is being measured.

According to Clive Coffee's assessments, all three of these grinders have about 2.2-2.5g retention.

Likewise, each of these grinders have not only bigger burrs, but also different burr design, and different supporting features.

My experience with the v1 Original Atom (60mm) involved not only clumping, but clogging. It almost certainly will not be the experience with any of these three, but I note the 65 and 75 have additional anti-clump tech. That may be amazing wizardry OR marketing hoohah. Regardless, that plus the better burrs (from their Zeniths) would be compelling reasons for me to pick the 65 instead of the 60. Even if the taste difference from larger burrs is not obvious, it may offer more consistently good shots.

65 to 75 is similar to the above, though the 75 has Mythos burrs which people like a whole lot. The 65 is probably a great choice for you, and if you get the 75, that would also be nice

GregoryJ wrote:As someone else has said, the Niche Zero is a great option. I'm not sure why you say there are no good single dosing grinders in your price range.

But, it sounds like you're leaning towards hopper fed. When I got the Atom 75, I was under the impression that you could single dose or hopper feed it. That's not the case. Grind adjustments absolutely require 10g or so before they take effect. If you go into it knowing it's hopper fed, I think you'll be pleased. I wouldn't obsess over burr size of you're budget conscious. The Mignon Specialita (55) and Atom 75 tasted very similar to me with their stock burrs.

Grind adjustments don't require 10 grams from hopper fed on a doserless grinder. There's a few tenths of a gram of retention, but that retention is the entire memory effect.

That's what I found when trying to single dose it. Putting 5g through wasn't quite enough to make the next 2 shots identical, but putting 10g through was.

That doesn't make any sense.