The results you'll get between the 2 systems will vary greatly. While I no longer shoot with a 503, I found its TTL system very limited compared to the Nikon TTL system. You're far more likely to get less balanced fill with the 503 TTL system. I personally feel you're better off using Nikon TTL, but shooting the Hasselblad with the Metz in manual mode, and just using appropriate light modifiers.