i so often shoot in low or marginal lighting that i value the ability to gather more light more than i gather the ability to zoom. i can almost always walk closer to my subject. (i don't do birdwatching.)
if your regular subjects are far off and in daylight, sure, go for the 80-400. but me, i do close-ups and medium, so i want light and optical clarity more than ultimate zoom.
no subject
i so often shoot in low or marginal lighting that i value the ability to gather more light more than i gather the ability to zoom. i can almost always walk closer to my subject. (i don't do birdwatching.)
if your regular subjects are far off and in daylight, sure, go for the 80-400. but me, i do close-ups and medium, so i want light and optical clarity more than ultimate zoom.