Merc 70 or Merc 115?

[WhalerSailor]

I have an old Boston Whaler Montauk 17'. It currently has a 1979 70 horse 3 cyl. Mercury. A friend of mine wants to trade me a 115 Mercury inline six for it (circa 198?). The boat is rated for a max of 100hp. I'm not sure whether or not to trade...I could use the extra speed, but I'm not sure about the sacrifice (Gas Milage, weight, etc.) Anybody have any ideas? <br />Also, does anyone know of inherent problems of either that may weigh in this decision? Thanks, Dave