I lusted after the Canon 500mm f4L IS for years. I saved my pennies and waited and waited and finally bought one about 6 months ago. At the time, I had only shot crop sensor cameras and mainly my 7D. Then I moved to full frame, and I don't ever want to touch my 7D again. The unfortunate side of that is my 500mm now seems shorter than my 400mm f5.6 did on my crop camera. I know I can slap a TC on it to make up the difference, but on top of a loss of image quality, I lose a stop and that defeats the purpose of this lenses.
Lately I've been thinking of trying to swap my 500 for a 600, but I'm just not sure I'm going to like that move. I've rented the 600 before and it's a nice lens, but the size and weight difference has me wondering if I will regret it. I can handhold my 500 all day long and not break a sweat, it fits easily into a carry on luggage and in the overhead bin on a plane, I'm extremely happy with the image quality of it, but I'm sure the 600 will match it. I can sell the 500 and pretty much fund a 600 for about the same price or just a couple hundred dollars more. I'm just not sure if that's the right move.
I mainly photography wildlife, birds and aviation. The 500 is perfect for aviation on my full frame, but when it comes to the wildlife and the birds.. it's starting to feel too short again. Moving back to a crop camera is not an option for me at this point. I'm addicted to the full frame quality. What should I do?