I'm sure the OP has already decided what to do, but in case anyone else is reading this, I'm posting this reply.
An additional 1 month mortgage payment applied to the principal DOES NOT take 8 yrs off a 30 year mortgage. Use any of the online mortgage calculators (like this one: http://www.hsh.com/calc-amort.html ) to see the effect based on your specific mortgage and when you are making the extra payment. In the test I ran, with a 350,000 original mortgage and an additional $1987 payment right at the 5-yr mark, this took 3 months and $5830 off the 30-year mortgage. [Steve, whoever you are, I hope your signature doesn't mean you are in finance ... or maybe I should get my mortgage from you & make a few extra payments!]
Whatever you do, make sure you check with your lender BEFORE you make the additional payment. You should be very clear about how you want the additional payment applied. Unless you specify (& it's allowed under your mortgage rules) you may just end up prepaying an additional "regular" month. If it doesn't save you time & money, you may be better off investing that extra cash.