The weight difference is 25 lbs being the 4 the heavier. the speed is apx. 4-5 less for the fourstroke, and the hole shot is a little slower. That being said I am not a speed freak. As far as the cost of the oil for the optimax how much it would cost for the year I have not a clue. I will probably fish 5 times a month. I was able to test drive a Lowe stinger HP18 yesterday with a 115 optimax pro xs. This boat was extremely stable and had a great hole shot, and very comfortable at a top speed of 56-57 on the speedo. I think the actual speed is around 52. So all that said would the cost of the fourstroke per year be cheaper. Cost of motors is 125.00 extra for the fourstroke total.