I think this is where internet conversation breaks down. What you just said *sounds* generally right, but from experience I tend to wait and see since the vast majority of people who say they're doing tanren of some sort appear to be mostly arms when I get a chance to see in person. Not to judge or imply anything; only saying that IME this is something to watch out for. Keith made a good comment about taking out the slack... how people take out the slack, etc., is important here.
I've seen a good axeman cut a number of paper-thin shavings off the end of a green log, but I've never seen a western sword-enthusiast do the same thing.
Sorry Mike, I checked out of this guy for a minnute. I don't know if I would go as far as to say the lighter suburito are good for tanren, but I do like them for form. I think many of the exercises we are discussing are probably better with a lighter suburito, rather than the heavier version. I tend to like the heavier suburito for centering and body unification; I like the excellerated fatigue from the heavier weapon and the reliance on body structure. We have several students strong enough to cheat with a lighter weapon who get fatigued with a heavier one. We often fatigue ourselves then move to a lighter weapon for training... I just heard a story about a class who's students were instructed to hold kamae for 30 minutes...ouch. That's fatigue.
Oh, and I am a total fan of the lumberjack games on ESPN 10 at 3:00 AM... Those guys (and gals) are serious and it makes me nausious to see them swing razorsharp axes inches from their legs. Not to mention wield a chain saw driven by a motorcycle engine...