Thanks for everyone's comments and general support which confirms my thinking is that too identical bodies/setups is hard to beat. As an aside ruggedness tests are not likely done by many intentionally but yesterday by accident my Z8 and 600mmPF took a hard drop from about 4 feet high and skidded along my drive way. After my heart started beating again I picked it up and the lens hood is scratch pretty bad, a small scratch on the hot shoe and after it was cleaned up I can find no other scratches dents or visible damage. I tested it throughly last night and I can find no functional issue at all. Please do not try this at home but hopefully it gives some comfort for others on the ruggedness.