The new growth is what generates the floppy conditions - the wood hasn't had a chance to ripen sufficiently to hold up those big, heavy flowerheads. I generally recommend pruning by half, leaving a portion of last season's growth intact to provide more support. If you do, I'd do it soon, as it is starting to get late in the season for pruning.

And I'm not sure I'd be overly concerned about it getting as big as 9 feet!! Pretty unusual for any paniculata to get that big (unless trained in a tree form) although you may very well see some additional height put on this season.

Thanks. There is already a good amount of growth on the top of the stems and if I pruned off half now, would lose all of it. I think I will wait till next year to prune.