As has been said above, neither of the boats you are talking about are serious steps up in terms of speed.
Nor should you be using your back to haul your boat, unless you are completely without a choice.
So you need to look at how you are moving the boat around, and ways to make that easier physically. That will give you more head room on the length of boat you can get.
So between car and water, you need a cart. Basic ones can be gotten for as low as $30. For loading on/off the car, you need to find ways to slide the boat up rather than lifting. This can be anything from a large towel spread out to protect the paint job to fancy stuff like the Amagansett Roller Loader and a third party system.
I don't know what rack setup you have right now so it is hard to tell what would work. But the right tools will allow you to focus on the boat you want to paddle rather than the one you can dead lift.
Touring Kayak Paddles
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