Yes the Pentax K-5 is a great camera, best in class for high ISO noise. But if you insist on comparing with Canikon, the available glass for Pentax is not the best. It may be harder to find what you like.
A comparison between zoom or primes is apples and oranges. Yes primes trend to be sharper because they can be simpler but there are many (expensive) zooms outperforming (cheaper) primes. But when you find yourself constantly changing primes, missing shots, whereas you could have solved the situation with a simple turn of the zoom ring, make sure you have some zooms as well.
Quality is expensive and this looks like a good one