So you're getting better. Sports, nature, scenics. Serious stuff. So now you've invested in some serious glass to support your creativity. The 300mm f/2.8 is your choice.
Now you have to figure out how to carry it on assignments, along with a body (and a spare, of course). It needs to offer instant access to your gear and when not in use, softly cradle everything to protect your investment. You need the Tenba Long Lens Bag LL300 II.