Dave Ramsey isn't the be all end all. I've heard him give bad advice before. You could take $90K and make more money than you would gain by paying off student loans at 6% interest. I like real estate, but that's an animal that many aren't willing to tame. I earn almost a 10% ROI on one property and I've gained about 30% in equity. Looking to add more in the near future.

DO NOT SPEND 90K paying down your wife's school loans. Like I said, there are much better uses for that money long-term for the both of you. If in 5 years you're still married, maybe consider it then. But depending on the type of account that money is in, you may be facing large penalties. Take the money out in a way that will penalize you the least amount possible.