There will definitely be a difference between 40K and a million poly model of course. However realistically a 200K-500K model can look just as good. It's all about shaving polys without losing the border detail to a noticeable degree. I think for most games to use poly assets north of 500K in real time at 30fps we will have to go to next-next-gen. But for this generation, we will see noticeable difference in terms of roundness especially as tessellation tech matures (especially if the more attainable Silhouette tessellation becomes ready for usage asap).
Let me remind thee once again, how drastically better Drake looked going from Uncharted 1 to 3 courtesy of shader, lighting and texture improvement.
Drake in uncharted 1.
However, as it stands, an 60-100K main characters will still look absolutely phenomenal. As such the focus will shift to things like cloth animations (so articles of clothing like a long cape or shawl do not look blocky while transitioning from shape to another or in general mitigation of clipping between articles of clothing depending upon the fold).