Question on Leica 50mm f2.0 Summicron - R

[Pascal]

Was wondering if someone on the forum could comment on the performance of the Leica 50mm f2.0 Summicron. I am thinking about using one on my Nikon D700.
How does it compare against a Nikon 50mm f1.2, or Olympus OM 50mm f1.2, or the Sigma 50mm f1.4 - sharpness, contrast, resolution, out of focus highlights, bookeh, etc.

Plus additional question: The filter thread on the lens appears a bit "not so standard". It appears this lens uses a Series VI retaining ring and a specific Series VI UVa filter for the ring - which being Leica are probably not very cheap. Is there a replacement UV filter that would fit on the lens - anyone know thread size.