: In the end, how much of a difference does weight (both of kayak and cargo)
: make a difference, and what exactly does it effect?
As Mike said the difference between light and heavy is just that,and what it primarily affects is your ability to lift something heavy or light. Given that the difference between a light kayak and and a heavy kayak might be on the outside 20lbs that amount could be a fraction of a 175 paddlers weight plus boat plus gear. 175+40(light kayak)+10lb(gear)=225. As gear and paddler weight increases then boat weight differences descrease as a percentage.

Without getting into the significances in handling that might come about with different weights of cargo and kayak the heaviest , the paddler, has the greatest affect,,not just because its the cargo defining the problem but because the weights of people bring the greatest variation to the whole package thereby having the greatest affect on handling differences, which are the differences that matter the most.

So for me in the end what matters is that a person is in a boat that they are not too light or too heavy for. What matters to you?