I spent some time with samples downloaded from site posted by David. And I compared noise level and disturbing. The result is:
ISO 200: without any NR, images from D3 are slightly less noised and look more pleasant then from D300. After NR I didn't see almost any difference.
ISO 800: without any NR, images from D3 are markedly less noised then from D300. But after NR I found differences only at wood surfaces etc.
ISO 3200: without any NR, images from D300 are heavy noised. And NR created a lot of small artefacts and color splashes in them. Images from D3 aren't too usable without any NR, but I think they have super look after NR.
The IQ at low and middle ISO can be one and only reason to buy D700 for me. But I still don't know yes/no...