well.. are you talking about a playboat, creeker, or river-runner..
What boat?
What are the sizes your stuck between?
How long have you been paddling?
some General knowledge: When you are close to maxing a playboat you'll be able to throw it around easier since you have more leverage over it.. However since you are somewhat sinking it, the playboat won't perform airial moves very well. for example:: the boat won't bounce off a wave on airblunts as high or have as much 'pop' out of the water in a loop. also, the boat will not be as fast on a wave if you are maxing out the weight range.
If you look at the suggested weight range chart, it's better to be smack in the middle, and if your not, go up or down a size or change manufacturers.
It's ok to max out the weight if your just learning tricks, but once you have the moves down, you'll need a bigger boat to do the trick some justice.