My Voigtlander Nokton SLii 58mm f/1.4, has across the frame sharpness wide open, along with fantastic color and contrast. It's just a manual Nikon-mount lens, but I really don't feel the need to buy another 50mm lens. Its focus confirmation works great, via the adapter. And the focus ring is a pleasure to use.
In my opinion, Sigma (or anyone) should make a faster lens, such as an f/0.9 in EF mount. That would be interesting. It might be worth paying over $2k (even for a Sigma!)...provided of course that it was decently sharp and focused well. Better would be a 95mm version, even at a correspondingly higher cost.