Something else is that I don't think the 5/1 ARM is much worse than the 5/5 ARM. What if interest rates are unusually high at year 5 but then go back down the next 5 years? You lose out.
So I check out rates because I was curious. Using aimloan.com (I just picked them because they have a great tool that shows a ton of rate options and costs), and your information for my county I get:
(Picking my favorite options. Closing costs include appraisal, attorney, title insurance, and everything else.)
30yr fixed, $2k closing, 4%
20yr fixed, $500 closing, 3.875%
15 yr fixed, $1700 closing, 3.25% ($2500 monthly payment!)
10/1 ARM, $145 closing, 3.625%
7/1 ARM, $600 closing, 3.375%
5/1 ARM, $800 closing, 3.125%
So I think you should definitely refinance if you can get rates like these. But of these options, and given that you could be in your house for over 10 years, but expect to be gone before 15 (assuming I understand your situation correctly you'd definitely FIRE and have moved by then), I would do the 15 year fixed. Your payment would not change, but you would be building equity at over twice the rate (1/2 the term and lower interest rate)!