I have a 33" spread on my '09 Impreza. With bow and stern lines and Yakima cradles that has been fine for my touring kayaks. For my longer racing kayaks I use a GoodBoy Vee rack (http://goodboykayaks.com/) that mounts to the Yakima bars and gives a rock-stable 8 foot spread: http://www.gregstamer.com/wordpress/wp-content/uploads/2013/01/GoodBoy_Impreza.jpg.
The Vee rack also works fine for my narrow sea kayaks (all are under 21" wide), however you do have to lift them higher to load as compared to Yakima cradles.
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