Once again I have assured myself that if turns out to be too heavy to lug around [it weighs in at 11.8 lbs!] or I find I don't put it to good use often enough it can be sold for very good money. I have done the usual refurb with Canon paint to cover up the inevitable chips, so it looks like new again. I will endeavour to find a manual on ebay, it will then be complete & as new, probably making it worth quite a bit more that I paid for it.
So far I have found it to be an exceptional piece of kit, it does weigh a lot more than the EF500mm, but with the 1.4x Extender attached the EF600mm comes in at fully functioning autofocus 840mm f5.6 on a 1Ds Mk III or close to 1100mm on an EOS 40D.