To replace or augment Sigma 70-200 OS?

Well, I took the plunge and bought a Nikon 70-200 f/4G and couldn't be happier. The difference in image quality (to my particular copy of the Sigma) is night and day, in addition to the added 'X-factor' that the Nano crystal coating gives. Having owned several N lenses now I've come to recognise the unique rendering it gives and I'm totally hooked. Nikon has an absolute winner in this lens - so much lighter and easier to handle than the f/2.8 lenses.