Sorry Jay, didn't mean to be flippant there, I should have just said there's always a chance it won't sell right away. In the current market, a lot of good houses are sitting on the market while everybody is looking for the deal of the century. I'm assuming in 5 years we'll be back to normal, but assuming something and than making an invesment based on that could be risky.
I'm not sure what the current stats are for home sales in Indiana, but a fair guesstimate would be 3 - 5 months listed on the market before it's sold. Most people do not sell their house within a month or two. Look at the worse case scenario for how long it will take you to sell it and what the payments will be when the rate starts to adjust and compare it with your monthly savings by going with an ARM. You will have more flexibility in selling the home since you'll have at least 20% equity in the home so you can always take a loss if for some reason you can't sell it at fair market value. But once again, who knows what your home will be worth in 5 years.
You will have a cap on how much those rates can adjust, so as long as you're okay with covering the first year's worth of adjustments, than I think you've sufficiently covered the worse case scenario.