FWIW what I was taught is that the suburito (that always makes me crave Mexican food) shouldn't be overly heavy. Just heavy enough to give you better feedback. So it's not like you're trying to strengthen your muscles so you can swing harder. It is a means of learning to gain fine control over a heavier weapon. Over-extension, over-commitment, trying to muscle a cut, trying to muscle-stop a cut, etc. all result in bouncing, bobbling, etc.
But YMMV. I really don't know. Just another data point for you as it is what I was told.
So form, form, form. With smoothness come speed and power, not the other way around.
To that end a training blade isn't a bad way to go as well, its heavier and sure lets you know when your cut isn't through wobble and sound...costs a bit more though ;(