Strongly considering selling the Canon to fund the Tammy! I want to plan a trip to Yellowstone this summer, and the extra reach would be nice.
Order it, use it. If it does what you need, then you have your answer. If it doesn't do what you want. Return it. And you still have your Canon. If you find yourself not needing the Canon after having it and using it (the Tamron) then you simply sell the Canon and recoup funds.