But I need some advice: For the high school graduation of one of my sons, I am looking for an Camera. He likes to photograph birds and planes, and now landscape at climbing.
For birds, you *don't* want a full frame camera like 6d or 5d3 because crop cameras have a 1.6x longer reach - that's why birders that don't want to spend $10000 on a lens have the 7d.
(I owned an 7D, but when I photographed with it, I did not use the continuous shooting mode. After it crashed, I use an 60D. But my son tells me, that the 60D takes a lot of time to save the images when the buffer is full. Sometimes he is not able to shoot another RAW series of 10 images for 3-4 minutes.)
I've got a 60d, and 3-4 min is certainly an overestimation, though the buffer of the 60d is not as deep as on the 7d and the 60d/7d don't support the newests/fastest sd card standard. Anyway, for landscape and climbing, and even for wildlife you don't necessarily do spray'n pray but take selective bursts, so I've never found the 60d buffer limiting myself - and for action, the 6d is for low light shooting and would be a step down (slower fps, worse autofocus).
My advice, even if you are planning to do differently: Use the cheaper 7d/60d and get a good lens like 70-300L or even a tele prime, it's the lens that takes the pictures.