Instead of looking at it in terms of what interest rates *might* go to at some point in the next 10 years, I'd look at what YOUR current interest rate *could* go up to. Is there a cap on how high your rate could ever go over the life of the loan, or is it strictly prime minus 0.75% no matter how high prime might be?
Assuming there IS a cap on how high it could be, that's the rate you need to look at. Let's say the very most you could ever pay no matter what prime went to was 12% (just making up some numbers here). What does that do to your payment? Could you afford it?
If you look at your maximum interest rate and could afford it, I'd likely stick with what you've got. That's saying a lot coming from me, the one who absolutely detests ARM's and thinks they should be outlawed altogether.

One huge factor in me saying this is the fact that you have 10 years or less left on your mortgage, so you should at least in theory have equity that could make refinancing easier if it absolutely came down to it.
Now, if you look at the maximum interest rate and think "Holy crap! There's NO WAY!", you need to get a fixed rate ASAP. If there *is* no limit to what your interest rate could go to, you need to get a fixed rate ASAP. Basically, if you can't afford the worst case interest rate, I'd get out. Like yesterday. You have absolutely no control over what prime rates are, and while we can all make educated guesses, that's all they are. Guesses. And the roof over my head needs to be a bit safer than a guess, kwim?
One of the biggest problems with an ARM is the assumption that "I'll just refinance" before the rates go up. Well, what happens when the banks aren't lending or you can't refinance for whatever reason? I can't imagine EVER going into a mortgage with the thought of "I'll just refinance at a fixed rate", assuming that everything is going to line up perfectly and it'll all work out as planned.