re: Mortgage rates trend for the rest of the year?

We are planning to refinance our home. We are currently at 4.5% on a 30-yr fixed and want to switch to an ARM. This is a starter home and we don't expect to stay here for more than 6-7 years. In this situation would you rather go for a 5/1 or a 7/1 ARM? Obviously the rates are better for the 5/1, but I fear it might be a little to aggressive. But when I look at the rates for 7/1 vs our current 30-yr fixed, the 7/1 will only be about $225 less per month and I begin to wonder if that is enough of an incentive to switch to an ARM. It is so hard to decide what is the right thing to do and I have come to the MB for help.