An honest appraisal of the Nikon D300. Link.
If it weren’t for the existence of the D3, this camera would be on my lust list, what with it’s live view, 51 focusing points, ISO capabilities, etc. Is it worth it for the overall image quality? That’s tough, because most likely you aren’t going to see a dramatic improvement in that regard, but yes you’ll love the features.
It’s hard balancing what you need with what you want sometimes. (Some might argue that one doesn’t “need” the D3, but that’s not true I do NEED it, at the least to quell my absolute jealousy of everybody getting theirs on pre-orders right now.) Anyway this a theme discussed in Camera Labs verdict which includes helpful comparisons to the now usual suspects including a Canon fave 5D:
For only slightly more than the Nikon D300 you could buy the Canon EOS 5D. The D300 trumps it in every respect bar one: the full-frame sensor. As you can see in our Nikon D300 Noise results, the full-frame Canon 5D may share the same resolution, but the bigger sensor allows it to out-perform both the D300 and Sony A700 at higher sensitivities.