The first order effect is the number of cell banks in parallel. The smallest batteries use 1 bank of (5) 3.6V cells. If you look at the batteries from any manufacturer, you will see sizes like 3AH, 6AH, 9AH, and you can infer that these have 1, 2, and 3 banks of 5 cells in series. Just like having 1, 2, or 3 horses pulling a wagon, you can get proportionately more peak amps from more banks of cells.
You can also get bigger horses, and put them in parallel, and pull even harder on the load. That is what the HO batteries are.
If I were looking, I would get the biggest capacity, and see if that performs for you. A large battery has an additional advantage, in that you probably won't cycle it as deep. Going from 0-100% charge ages the battery pack, and over 100s of cycles, you will lose some capacity. If you don't go to 0 every time, they last much longer. If you don't charge to 100%, even better. I charge to 3 bars out of 4, and still have 1-2 bars left on a 9AH when I get home.
If you have problems with cutouts and stalls, you may need the HO for even more pull, but I have not heard of issues. The worst case will be when the batteries are very cold, which decreases performance.
The other thing to consider is whether you want that fast charging. Pushing the power in faster generates more heat, and degrades the battery faster than charging slowly. Since for fishing we generally go home at night, 8 hours to charge is no problem. The new faster chargers would just put more stress on the battery for no benefit.
