Need advice re long telephoto lenses

Of all those I prefer the Sigma 100-300/4. More versatile than a 300mm prime and hardly any drop in IQ (actually scores better at 300mm than many primes). And with a good 1.4x TC on it still produces very good IQ. Street price if you can find one is around $700-$800. Finding one in Pentax mount is the main issue. Think of it as a longer 60-250/4 with the same IQ but no weather-sealing.

Kent Gittings