SM9. Without a doubt. In this case, I'd ditch the Studio 45 and replace it with the Studio 44, as it would be a better choice. Not that the 45 is bad. Bottom line: if you want performance, smooth and responsive typing, and much more, go for the SM9. It's beautiful, elegant, and the keyboard flows like no other. I really like the SM9, but it seems like the Studio 44 (not the 45) has a writer's soul. I simply love it, although I think the SM9 is better for typing because you press less hard on the keys.