Well I am sorry to say that I wouldn't count on it arriving before you move. There are quite a few of us that ordered on June 5th that still haven't received our MBPs. In fact some have actually had their estimated ship date delayed and we were already waiting 4 to 6 weeks. Maybe if you ordered before you moved and it hadn't shipped you could just change the shipping address without having to pay additional taxes. I am not sure how that works. I wouldn't really think changing your shipping address would change the cost once ordered, but I am just not sure. You could just tell them the reason for the change in shipping address was due to an extended vacation or visit. Good luck!
The tax rate may be higher in your new state, but you would only be charged sales tax on an online order if your new state has an Apple Store, I believe. Judging from the fact that you're going to a state whose rate can be twice that of another, I'm guessing you're moving to a state with several Apple stores...
Good luck -- I wish this forum thread didn't exist (i.e., there wasn't a ridiculous delay to speak of!).