Full frame or not full frame?

I'm wanting to switch over to full frame from dx, but the only thing holding me back is that I do wildlife photography. I will be either buying a Nikon D300 or a Nikon D3 to go along with a used 500mm f4, that I'm getting cheap from a friend.

I shoot alot of wildlife, at the moment with a Sigma 100-300mm f4 plus teleconverters.

I also shoot sports such as skiing, skating and surfing and so full frame is great for these, but because I shoot wildlife, will I regret not having a crop body for extra reach.

Also I have watched alot of wildlife photography videos and people seem to shoot with full frame… Is this the norm?

My question is whether it is better to have a full frame and teleconverters or a crop censor body?

If you're asking, you don't need full frame.

I can't think of a single reason why you would want full frame for what you shoot. I have a full frame and a crop frame canon. I use the full frame for landscapes, photos of stars at night, and macro. For any of the things you list, I'd grab my crop frame every time.

Full frame is better, quality-wise but you'll have to get closer to your subject. 1.5X closer is really scary! No teleconverters. They degrade optical quality. There's no standard. You can use APS-C and get the same results to most of your audience anyway.

You trade reach for extra resolution and better image quality, especially in low light. I don't know if the extra resolution makes up for the crop factor… But you have a 500mm lens. You should be in good shape either way.

I faced the same struggle when I was deciding if I should upgrade to a 5D Mk II or a 7D. Picked the 5D2 eventually, and haven't looked back from full-frame since. I love it.

Nikon full frame cameras can be used in cropped (DX) mode. So you can get the advantages of a cropped camera in the full frame camera.

One caveat however is the resolution is reduced.

For instance, with the D600, it is 24Mp in full frame mode, but only 10Mp in cropped mode.

And the D800, while it is 36Mp in full frame mode, it is something like 16~17Mp in cropped mode.

Of course this is to be expected as the cropped mode is using less of the sensor.