I am hoping to Oder some apple trees soon, and I’m trying to decide on the best rootstock for a small space (30x40 with most of the center taken up), with somewhat water retentive clay soil. A friend suggested b9/m111 or m9/m111 interstems, since they are somewhat size controlled, but the Geneva dwarfs are easier to find.

Does anyone have experience with these? Are they different enough from the Geneva dwarfs to seek out? Do they anchor as advertised, usually creating a free-standing tree (Not essential but nice)? How do they hold up on wet soil? in less soggy months, do they need a lot of extra watering? In short, are interstems better at all, and if so, are they worth prioritizing over the g series?