For me, the debt isn't worth the rankings unless you're guaranteed to get a high paying job post-graduating, and let's be real- in this economy .. ? is anything guaranteed?
Especially if you work for an NGO or a non profit, you'll have to start repaying the debt as soon as you graduate, and the time it might take you to pay off 90K as opposed to 40K might interfere with getting your PhD later rather than sooner.
I personally chose the undergrad institution that offered me the most money, and I'm graduating this year with only 3K in debt. Looking back on it, it was a pretty tough decision for me- but considering how the economy turned out and my roomies are struggling to find jobs once we graduate, I'm very thankful that I did make that choice.
Just ask yourself, is the debt worth going to the #7 school or not? That's what it really comes down to.
Hope that helps :/