I have recently grow an interest in sports photography...
First we have to exclude the new Canon super teles as they are EXPENSIVE!!! It's true, I can't afford them no matter how good they are.
So the choices, the EF300mm f2.8 L (non-IS version), the EF300mm f2.8L IS(first version), EF400mm f2.8 II(non-IS) and the EF400mm f2.8 L IS, all second hand of course, since they are all been discontinued. And if someone could give a comparison of the first generation IS super teles to the latest one on AF and IQ that would be fantastic!
Mainly for hockey, football, basketball and soccer. I already have the 70-200mm f2.8 so yea. Body I will be using will probably be a 1D IV I will use my 1Ds III if I have to......
I shoot sports and I use the 300mm f/2.8L IS (Version I) and a 1D MKIV. This lens is very sharp and very fast and it mates wonderfully with the MKIV. On the MKIV you will have a 35mm FL equivalent to 390mm, then just add the 1.4X for 546mm f/4 for Football and Soccer. I can shoot the 300mm on the MKIV at night @ f/2.8 and 1/1000sec between 6400-12,800 ISO without any problems depending on the lighting on the field. If you can shoot 1/800sec, it's even better. Slight noise reduction may be needed, but not always. If the game starts at dusk, I will start off with the 1.4X and as it gets darker I will take off the 1.4X if necessary. For day games, just add the 1.4X when needed and you're set.
For indoor basketball and hockey, the bare 300mmm would be good for opposite end shots. You may even want to use your 1Ds III for the indoor use. The MKIV is weather sealed and is more rugged for outdoor use and provides the extra reach for the larger fields. For outdoor night games in poor lighting you may need to shoot the bare 300mm, so that you can keep f/2.8. The 300mm is great on a monopod for field sports, and it's also definitely hand-holdable. It's also a lot cheaper than the 400mm version I.
If you've never handled the 400mm Version I, then you're in for a shocker. You'll definitely need a monopod for this one. The 400mm f/2.8L IS Version I is a great lens for field sports, but it is pretty heavy and a bit long and cumbersome for indoor sports. It's also quite a bit more expensive than the 300mm f/2.8L IS.
The 300mm f/2.8L IS Version 1, is cheaper, lighter, hand-holdable, better for indoor sports, and more flexible than the 400mm.
Get yourself a nice monopod, knee pads, shoot low and you're good to go. I would put your 70-200mm on your 1Ds III and the 300mm f.8L IS on your MKIV and you are done!
Generally speaking for fields sports, a good FL would be between 400-500mm. If you're too long, you'll start missing shots and cutting off limbs. You could always crop a little.
For a 7D (1.6X) I would go with the 300mm f/2.8
For a MKIV (1.3X), I would go with the 300mm f/2.8 with or without 1.4X.
For the newer FF Bodies (1.0X) I would go with the 400mm f/2.8 with or without 1.4X, or the 500mm f/4.
With the new and improved noise control of the new 5DIII and 1DX, I predict that the 500mm f/4L will become more popular for field sports, because a lot of sports shooters are using the MKIV and 400mm for 520mm. Now with the new FF bodies, their 400mm will only be 400mm, or they could add the 1.4X for 420mm f/4 and slow down auto-focus by 50% and decrease IQ, or they could opt for the 500mm f/4L and maintain a faster AF and retain IQ.