Heaviest ballhead? Probably pretty darn heavy. Take the max load capabilities of your tripod and subtract 4 pounds to account for camera & lens weight, and that's your max head weight.
But really, how do you use the tripod? Do you like it fully extended with a big camera and lens on it? This might be precarious with a light tripod - stable, yes, but kick a leg accidentally and it may fall over - or it just might not be heavy enough to remain motion-free. You might not want to decrease stability by adding a heavy head. Do you always use a small lens, thus adding little weight and allowing for a heavier head? Do you like to do landscapes low to the ground? Stability's not so much of an issue here, so a heavy head's OK. Did you get the CF to save weight? If so, get a light head.
I guess, for me, the answer would be to get the smallest, lightest head that will do what I want. I say small & light because that's why *I* would buy a CF tripod.
Actually, I think the answer for any "which head" question is "the smallest, lightest head that will do what you want." But with the reminder that if you use big lenses in high winds then the "lightest" head should probably weigh as much as possible. And then you wouldn't want a CF tripod in this case.


