Should I jump the Nikon ship?

IF you are total concerned about just this specific shooting scenario, Go with a Canon 1DIV 16mp files a 1.3 crop and 10 fps. I would go 500 or 800 but for wieght avoid the 600. ANd you gonna need a gimbal head! Either rent it from Lens rental or buy it used from KEH. You have a 14 day grace period with Keh to return for any reason. Their bargains are ussually in excellent shape. You get 6 month warranty and can buy a 3 year extended warranty from them.
Canon has a great focusing system.