That's what i was saying, there is one DX11 release for all gfx cards ATI, Nvidia, Intel, Matrox, and others, DX is the same for all manufacturers, and all gpu's, therefor it will look exactly the same on all of them.
Now, tessellation is another matter, i assume you are all aware of what it is and how it works, the more powerful tessellation engine will yield smoother meshes with more polygons.
As for color, all monitors, as do gfx cards work with 32 bit color, simply because there is no advantage to producing more colors, in other words we've reached the limit of color reproduction.
If you really care about visuals that much, you it would be easier to justify the purchase of an S-IPS monitor, rather than a GTX580 vs a HD6970. my PVA panel is a million time better and brighter than my TN, if you are interested i will recommend you an HP LP2475w, or you can go all out and purchase a LaCie or an NEC.