i usually tell people that just about every lens made for the better cameras around are really really good, and that Nikon should be.
Think of it this way: If Perfect is 100, then the lenses made by leica and nikon in the 1050s were probably 95 or 96.
Modern computer generated optics are probably 98 or even 99, but that's still an awfully small difference. The difference between that Nikon and a Summicron might be less than you imagine since, if they were made at the same time, the Leica optic probably was assembled using Leica's famous tree-sap glue (really!) which may not have aged as well as whatever Nikon was using.
When pondering the difference between a lens that rates 95 and 96, keep in mind that the quality of the glass is only about 5 perent of the deciding factor of whether your images are any good. You are the other 95 percent.
So, go shoot, and be at peace.