Thanks. I've been reading around and I've seen one or two references to CA being present on D800 images despite auto-correction - so I gather from this that auto-correction is marginal and that what I noticed with my 28mm is to be expected. I suppose that I was bit disappointed - but there you are. My fault. My expectations were a bit too high.
So far as lens balance is concerned, yes, I walked into it, rather.
It's the first 300mm lens I have ever owned and I never gave the issue of weight the slightest thought. Silly me - esepcially when I held off from the D800 in favour of slightly lighter FX kit.