How much longer?
If you're looking at staying there 5-10 years, I'd say refi to PenFed's 5/5 ARM with no closing costs. Initial rate is 2.625%. After 5 years, it will adjust, but no more than 2% higher (so ceiling of 4.625%), and will stay there for the next 5 years. After that 5 year period, it can rise again (again, max of 2%) for the next 5 years. Total interest rate ceiling is 6% above initial rate.
If you're looking at staying there 15+ years, get a fixed rate mortgage. Find a desirable combination of rate and closing costs at a lender like Amerisave, Aimloan, Firstib, NMA, etc. Check your local banks and credit unions, too. But, in general, I don't think the differences in rates between ARMs and fixed rate mortgages is enough to compensate you for taking on the interest rate risk.
Waiting until 2016 to decide what to do is also taking on interest rate risk. Again, the spread between ARMs and fixed isn't enough to compensate you for this, IMO.
As for whether to pay of or pay down the mortgage, be sure to read the Wiki article: http://www.bogleheads.org/wiki/Paying_d ... _investing
. I'm coming around to livesoft's argument that there is additional value in the call option you have in keeping a mortgage (i.e., you can decide to pay the mortgage back at any time), which justifies keeping a mortgage even if your after-tax risk-free rate of return is lower. Plenty of threads here on the great "pay down or invest" debate.
Don't assume I know what I'm talking about.