the tamron is slightly better the the canon 75-300mm, but they are both low end lenses and are really not that good. The tamron is the best form the bottom of the barrel.
The kit lenses of the pentax are much sharper in the long end, and focus very fast. That is the lens I took the bird shots with.
But the pentax seems to be the best fit for your wife and you. Go with it. It is a great camera.
Super Frequent Flyer, no joke. Ex Patriot and loving it.
Canon Eos 60D, T1i/500D, Eos1, Eos 630, Olympus EPL-1, and a part time Pentax K-X shooter.