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Burlington may have more eagles, but if you are making that long of a drive and only have time for one location, LD 14 is your destination.
LD 14 has the capability of giving you both flyover and fishing shots, whereas at Burlington you are farther away from fishing eagles, but will get flyover shots.
I have a 400 mm lens and a 7D and find it to be great for both fishing and flyover shots at LD14. You may find that you are too long if you have the 500 on a 1.6 crop body. That is how close you are to the eagles!!!!! You won't need the 1.4 on the 500, unless you are taking static pictures of eagles in trees next to the parking lot.
You are basically positioned on a long boardwalk, immediately next to the downriver side of a lock. Eagles perch in trees on the other side of the lock and swoop down for any fish they see immediately in front of the boardwalk. The planners of that place couldn't have designed it, knowingly or unknowingly, any better. Fantastic!!!
The winter sun will make shooting better in the afternoon, when it is at your back or to the downriver side of the lock. I've found that the best shooting is with a southern wind, when the eagles pick up fish flying downriver into the wind and into the afternoon sun.