A used D-FA 150-450mm probably wont be cheap, even in used but good condition - if you can find one. I bought a new one and used it for my kids sporting events and I've used it
to photograph an airshow this year. The pricey lens is worth every penny and every ounce of heft. Focusing speed is good for these kinds of events. Image quality is excellent. Set it to f/8 in daylight and shutter speed at ~1/2000th using TAv on your K-1. You won't be disappointed in the setup.
Adding a new camera system + lens sounds like fun but be aware of what it takes to maintain and use two mounting systems. You will need to learn the camera, its capabilities and limitations, and learn how to process the images too. The Canon will produce images with its own seasoned colors, contrast, saturation, noise, etc. There is more than just dollars behind the decision.
If you're already thinking of a second system then have you checked out what you can in the u4/3 ecosystem? Many users have successfully created wonderful wildlife images. Camera bodies and lenses are smaller and lighter. The lenses are also very sharp. Maybe a used u4/3 setup could work for you too? Noise levels are a little higher due to the smaller sensor but that may not matter much if you shoot in daylight anyways.