Upgrade to FX Pro gear - is it worth it?

Barnie,

if you have loads of cash by all means go for the holy trinity; but if you have only money don't forget the other rule: invest in glass!

 A 2.8 lens means that you can get an image under certain lighting conditions which is beyond a slow lens. But I have also discovered that if you need a fast lens because the lighting is low, and the circumstances dictate you don't use a flash,  the chances are that it is also too low for the fast lens as well.  But a fast lens will always give that extra edge IMHO.  I have a 50mm 1.4 for my d300, and although the lens seem to be a bit slow to focus I do not get better pictures from my 18-200 3.5 zoom when the lighting conditions are zero: it still needs to focus, and modern cameras do not come prepared for manual focus (split screen). 

Yes there are advantages with having a D3s one of which is the high iso. But also these cameras are built for what they can do after the images is taken, or the ability to withstand high volume regular punishment. As far as the image is concerned probably the difference is not that much; certainly not worth the money for just this one feature. For the other features maybe. 

Whilst it is not all hype, and the advantages are real ones, it is also true that you need to learn how to get the best photos with the camera you have, whatever that camera is.

best

Lawrence