This is just something you need to work out for yourself. Personally, I have an Apex 9' roll-up and it's "rating" is 8hp. I have the following motors which have seen the transom. 2hp Honda, 6hp Johnson, 9.9hp Johnson. The 9.9 is the best choice in a true tender mode, covering modest distance at a fair clip. In dink mode, the 2hp is perfect getting, crew, and supplies from the dock to the boat in protect anchorages. The 6hp is the worst of both, weight of the 9.9, external tank and it will not plane. So what gets used the most? The 2hp 95% of the time. The ease of handling trumps the need for speed. If I were in the habit of anchoring in open roadsteads my choice may be different. In protect harbors my choice seems obvious to me.
RichH hit the nail on the head and carries the option on board.
I never tow in open water, period. its just bad JuJu. The bottom gets yucky, too. It takes 12 minutes, by myself, to hoist, deflate, and store the Apex lashed on deck with the motor on the pushpit. Interestingly, I have a hard dink with oars I use around home and storing the 8' oars is more challenging than the little 2hp Honda, on board.
One option is to service and sell your motor then get what you want. Good motors are like commodities, selling and trading fairly painlessly. I currently have the above mentioned, two 15s, and a 25 in the boathouse. I buy and sell all the time. I'm looking for a 4hp johnson with integral tank and F-N-R. I will sell a couple off to
balance the stock.
Good Luck!