9.9 is the best size.

2 cycle weighs about 75 pounds.
4 cycle weighs over 100 pounds.

2 cycle is good for an emergency backup, but if you plan on trolling for many hours of use -- 4 cycle is probably worth the extra initial expense and weight.

Extra portable tank is still good to have on hand if a fuel problem disables your main engine.

Why not stick with Johnyrude?

You tell me where the best deal is, and then we'll both know. ;)