In the world of sailboat auxiliary engines 9.8 hp is pretty powerful. Many sailboats do well with a 6, 4 or for smaller boats 2 hp. What can it do? Probably drive your boat at or near hull speed. But you won't drive it that fast. The outboard will be much more fuel efficient at about 3/4 hull speed. What it can't do is drive your boat into a choppy head seas as sometimes exists in the Sounds of the Carolinas with that efficiency. You'll move forward but at reduced speed and not too much comfort. Those are days to travel in the AM when the afternoon breezes have not yet kicked in. But that's true for larger boats and inboards as well. There is considerable current in some of the canals and rivers that make up the ICU. You just have to subtract the current speed from your speed through the water. Reving up the motor won't make a difference or not much of one. I'm not sure a bigger motor will. If you got a 15 you'd be burning more fuel all the time or running the motor at sub optimal RPM.
You do want to make sure you have the long shaft version, if it exists for that motor, so the prop spends more of its time in the water driving the boat.