> .... the D300 is great for >the equestrian events but in poor light struggles sometimes >and I hate using it at 800 ISO and above, which I had to quite >a bit on a recent trip to India.
>Do you think a D700 would give me enough benefit in the ISO >department to make a change?
I shot with both the D300 and D700 for several years. Sold the D300 recently - kept the D700. The D700 has a full stop better high ISO performance over the D300. So if 800 is your max on the D300, you would be happy with 1600 on a D700.
I think you are being a bit conservative with your ISO settings on the D300. I found 1600 to be good and 3200 acceptable. On the D700 I go to 6400. Viewing at 100% does not give a realistic sense of noise levels if the image is to be printed or posted on the web. A 50% view provides a better approximation. You might find you can go higher with the D300.