I use the D3 and 70-200 VR combo at f/2.8 all the time for concerts. I've never had a problem. It's an amazing combination. Bear in mind I'm tracking fast moving singers and guitarists too - the lens very rarely ever hunts and it's more about me not having the focal point bang on the eyes or shutter speeds dropping that spoils shots.

The TC14E2 is supposed to work brilliantly with the 70-200, TC17E2 pretty well and TC20E has very mixed reviews on degrading image quality. I'm taking a 17 and a 20 on safari next week that I've rented as the 70-200 is the longest glass I've got so we'll see what the quality is like.

I also shoot at ISO 800 + too...again, no problems with quality.

Cheers, Neil