As far as I know when reading, V3 will grow about 20 to 25% standard size, Ottawa 3 about 35%. How are you doing with hardiness on your Ottawa 3? This one is borderline for your zone.
What is your general objective,.. are you limited in space?
I'm not a fan with dwarfing....short lived and not so good in drought....I don't water.

Hi Konrad! I live in Brandon, Manitoba. Never had an issue with Ottawa 3 rootstock. I do have limited space in my yard and have tried grafting varieties. My goal is to have smaller trees as not to have as much shade in the vegetable garden. Favorite apple here is Norda and prairie magic, Minnesota 447. I also have a crabapple rosybrook(sp?) as a pollinator. Love. Seeing your posts and pics of your orchard.

Thanks Kaya!
I guess then V3 would be the one to try out, can you get the root stock locally? You can trellis to keep them low. Norda and Norkent, I have them both and very similar, infact I don't even see a different, I.M.O. these are still the best tasting apples and good keepers. You might enjoy the early Norland, ...just lovely right out of the tree, they're not a keeper so don't grow too many. Sounds like your'e on the right track!