Hey Ryan,
I have ordered 14 apple and 2 peach trees from Cummins over the last couple years. They have ranged from #1 (feathered) down to #4, which is a 7/16" whip. The three #4 grade trees were two apples and peaches each.
These two peaches have been a disappointment for me, in that they’ve only grown to 3ft and 4ft in two growing seasons. They did better this year after fertilizing them, whereas I didn’t fert any trees that were planted last year. Now it may be because the soil is poor and acidic, and that doesn’t help peaches. I tried to remedy that with fert and lime, to get the pH up.
Of the two 7/16" apple trees, one is a Grimes Golden in G16 rootstock, and it has grown very well in two years, it’s put on some nice side branches and height and has even thickened up a little. The other tree is a Golden Russet on G222, and it has been the opposite- not a lot of new branches, still skinny, and it has already lost its leaves this year while most of the others have not. So a mixed bag with the 7/16 trees.
I have several 9/16 and 11/16 trees, and I think they have done really well. Good limb structures, good height, and thickness.
This year I planted a #1 grade Suncrisp apple on G30 from Cummins. Since it’s a #1, it had several short branches on it, which I pruned a little. It has done very well IMO for a first year tree. Good height, branches and thickness. The other two were a 11/16" (#2) Zestar on G30, and Alkmene on G11. The Z has done OK, has put on some vertical height, but not a lot of branches, while the Alkie looks almost as good as the Suncrisp.
I planted two peach and two pears this year from other nurseries, and they are all 5/8-3/4" thick. One of the peaches was a feathered tree, and it has put out good growth from the small branches. The other three trees have done decent.
To end this novel, if I had a choice, I’d rather have a tree at least 1/2" thick, with or without feathers, over a 7/16" or thinner tree.
Regarding roots, yes, if a bigger (by bigger, do you just mean a thicker whip?) tree is shipped with not a lot of roots, it’ll have a harder time getting established in its new home. If it’s a whip, it may have to be headed back quite a bit, if its feathered, those branches would prob need to be pruned as well. This is done to balance out the above ground part of the tree with its roots.
Some folks on here, who have vastly more experience than me, might say don’t head it back or prune it after planting. So there’s other opinions about this.
OK, enough from me!