keep in mind bigger files, more storage, slows workflow a bit/new workflow, can tax your current computer, does the software run on your laptop, etc, etc...theres so much more than just the back...
in my mind you'd be better off waiting to have $8-9k then spend $7k and have a $2k slush fund for what pops up.
just a thought.
PS - I dont shoot leaf regularly, but that those prices, you'd be silly to get a ZD.