I'm a live music photographer based out of San Francisco and am debating whether or not to make the big upgrade to the D4/800. The majority of the shows I cover are poorly lit, which is what music photographers have to deal with. I own a lot of fast glass, but I feel like the D3's AF system is just sub-par compared to the newer cameras that are out today. I've missed a ton of great shots because the AF wouldn't lock on, not to mention I'm almost always shooting at f./1.4/2. I rarely ever shoot above ISO 6400, so I am not really concerned about ultra-high ISO noise blablabla, as it doesn't concern me.
What I'm really asking: Do you guys think it's worth upgrading to the D3s/4/800 from the beloved D3? I'm open to the Canon system, as I could probably find some good trades?