the other thing to look at, with the interest only loans (going under the assumption the % only is for 5 years) ...someone had stated it gets people into houses they can't afford..that may be true now, but most people are planning on getting higher wages in 5 years...if you are planning on increasing your income, in the next couple of years you could do the % only, when you get a raise, take that extra income and apply it to your loan, thus cutting down on the principal..
the other thing to look at is, while rates will go up over the next 5 years, but will the refi rate be higher then then then the current 30 year loan rates are now...it will all be speculation, numerous things can happen, but if you look at historical rates over 5 years periods, you should be able to take a good guess...if you feel refi rates will be less 5 years from now then the current standard 30 year rates, then you may want to only pay % loan, and refinance in 5 years, at a lower rate, that will be cheaper to make your monthly payments and be paying on the principal