Originally posted by Northern Soul
aside from insanely high ISO settings, what would I gain over the D300? What would you do, and why?
Here's a link that will give you a very good side by side technical comparo:
Pentax K-5 vs Nikon D300 Detailed Comparison
Essentially they show the K-5 is a better camera in nearly every way other than, as other's have stated, auto focus.
After a lifetime of photography, what I've learned is that the biggest visible difference in my images was the lens. If I were you, I'd analyze what lenses I really wanted and could afford to acquire, and then go with the camera that best supports those lenses.