As expressed by Birna, the consensus holds that contemporary long Nikkors (G,E) outperform the vintage counterparts (AI,AIS)…in the immediate case, the 600mm F4s. While I cannot attest to IQ differences, I have come to appreciate the Nikkor 600 F5.6 (AIS) – around 7 pounds. Center frame results, when mounted on a D600, are resolute and satisfying for image size approximating 10 x 15 inches (24 x 36 cm). Is this enough: it seems like it, at least absent a modern G/E lens for comparison. Yst, direct comparison might be revealing: the 600mm E compared to a 600mm AIS trained on a common scene may well disclose discernable IQ differences. However, I would expect center frame resolution differences are small. It goes without saying, nonetheless, contemporary long Nikkors have much improved handling – vintage long lenses are impossible with fast moving subjects.