You can see if there are seasonal trends to pricing for any items you're interested in on CanonPriceWatch. Below all the vendor's prices is a historical price graph. Here, I can see the 300mm is at an all time low.

As for the Cameras... save a bit. Also consider the 5Ds in addition to the 1Dx. If you don't need sports AF, consider the 6D instead. It's kind of the Rebel of the full-frame lineup, but unless you actually need sports AF tracking, or fast burst rates, you can save yourself a lot of money and have an awesome camera.