Well, time for the old lady perspective.... ha, ha,, ha.
In attempting to get a handle on all this, which is really quite impossible with my brain, it seems intuitively that the limiting factor ultimately is the lens resolution. And degree of magnification of final product. And, I think I mentioned in the past I have shot billboards in the 60's with Hasselblads, and the magnification is around 240 X. They looked sharp.
But with the same lens, taking a DX size image to 10 feet wide vs. an FX sized image to 10 feet wide, viewed from 20 feet away, I would suspect this is when we see a difference. Maybe not so much in sharpness which is obvious, but in a lot of subtle differences in color depth, maybe in something like eyelashes, almost always a giveaway, and in geometric shapes with crisp edges. But shown by itself, my experience says the DX holds up just fine. It is only when we look at two images side by side we are able to say one is really better.
And, being a real ...... when it comes to criticizing photos, I see so much in the post processing which affects the final product, the DX/FX difference is often lost. And I am not talking about inexpensive shots... I am looking at post shoot errors in processing in mega buck shots, sometimes with big name clients. All these are things which make the difference between the two formats of possibly less importance.
Having said all that, the larger FX will most times be more forgiving simply because it contains more data. My suspicion is if one has larger pixels somehow this is better if only just for the fact they can gather more light.
But, when the new DX from Nikon comes around replacing the D300s, I think I might get this rather than another FX like a D800. The one big factor is with the long lenses... wow, 1.5 makes the 400 w.2x into a 1200mm f/5.6 which is amazing. And that is one enormous advantage from DX. It does bring up the argument of shooting DX on an FX body and I am not certain I have any thoughts about this.
So, just some more bologna to keep the thread going, chuckle.....