I know you issue all too well.
You are not going to get full image update rate from your existing system across your backplane. I would suggest doing an FFT on each image and passing up those results. As for your images, I would only transfer fractional portion of the images you are collecting. The amount you pass on is going to be based on the application.
Also, I don't know if they exist, but image compression on the FPGA may help with this as well.
I hope this helps.