I'm another Mountainsmith fan. I have three Day, one Tour and 12 Vibe II's (long story...).  The Strappettes really make the larger packs! 
I'm not too far behind on the Vibe II's - we have six.  One for each member of the family in different colors and 1 extra.  In our family we also have have two Tours, a Swift II, and a Clear Creek 20 backpack.  We're big fans of their products. 
The Strappettes really make a huge difference with the larger lumbar packs.  I recommend them too.