You can get the same shots with a D40 when compared to a D300. The D300 has the advantage of frames per second and you can push the ISO past 1600. You could look at the Sigma 70-200 F2.8, but I'd tell you to rent one first. Renting it will allow you see if you are able to get the shutter speeds you need(1/400-1/1000 sec). You don't want to spend the money on that lens and find out it's not quite what you need. If it doesn't work then you would have to move to the prime lens, and then that's when the D90 or D300 would be much better. The D40 doesn't autofocus with most prime lens.
I have the Nikon D40x and the kit lenses 55-200 ED VR but I cant get sharp enough photos with no flash and higher shutter speed. People I''ve spoken with tell me that I will never be able to get good shots with the D40. I have to get the D300 and invest in the 70-200 f2.8 lens. (as you know, BIG Bucks) Is it true that even if I spring just for the lens, the shots won't turn out as I'd expect or am I just dealing with camera snobs? There is another meet coming up soon and like to know what to do. What settings would you recommend as well? Program? Shutter Priority? Aperture priority?