Not when you're dealing with design. Maybe I should have been more definitive. Actual stroke vs. available stroke is what I was attempting to convey. Just because it's there doesn't mean it's used. Conversely, it doesn't mean you can't bottom out your sub either. What if you start clipping before you ever reach available Xmax? It's all dependent on power used vs. design.
http://diy-av.net/forum/viewtopic.php?f=8&p=594
Displacement is key.