Regular size Sophia is 14 by something, while the new smaller Sage is roughly 13 by 8ish. So I would say around the same size, but keep in mind that they are two different styles and their measurements can be distorted visually due to that. The Sage might appear bigger.
I like both. They are so different from each other. The Poppy is more neutral. The Kristin seems more summery. I love the textured detail on the Kristin. I am wondering if the Poppy leather is mottled looking like the pink and beige Poppys from last year, because I am not a fan of the distressed leather. It is funny because both of these bags were the ones I was drawn to in the Spring preview so I guess we have the same aesthetic. For me, even though the pink is beautiful, I don't think I would carry it. I would prefer a lighter, more subdued color.
Kristin!! It's such a beauty and the leather is wonderful. If it's the same size as the new smaller woven Sages (I think it is), it's going to be bigger than the small Kristin hobo and hold quite a bit more, but not huge like the original Sages.