for your use, my experience is that replacing the 5D with a 5D2, 6D, or 5D3 and replacing the 17-40 with any of a number of the better primes will make a significant difference in large prints - as will a good pano head, leveling base and L-bracket if you don't already have them. the AF, high ISO, etc. of the 5D3 will not be of much use to you - i only find a difference in IQ at high ISO. if you're interested in a good used 5D2, PM me.