Whether or not the K-7 is better than the D300 depends on what you consider important in your buying decision.
K-7 is smaller than the D300. Is that better?
K-7 has a more dampened shutter/mirror than the D300. Is that better?
K-7 standard focusing screen is easier to manual focus than D300. Is that better?
K-7 has interchangeable focus screens; the D300 does not. Is that better?
K-7 mounts nearly every Pentax lens produced since 1952 (including the much revered DA Limited primes); the D300 does not. Is that better?
K-7 adds image stabilization to every lens mounted on it; the D300 does not. Is that better?
K-7 with DA* 55/1.4 offer a full weather-resistant shooting rig for a mere USD$ 1950; the D300 does not. Is that better?
K-7 means that you don't give a monkey's toss whether or not other photographers consider you to be anything other than an amateur or hobbyist.
Is that better?
If any of the above are important to you, you'll come to terms with both the limitations and advantages of a Pentax K-7 system. Pentax can be said to be an "acquired taste". However, if you place great importance on blazing fast AF performance, full control of Dark Frame Substraction or great flexibility with proprietary flash lighting, then you're destined to become a Nikon man.
And yes, I once used to shoot with a Nikon system, albeit film. I tried to like the D300 when it first came out but that capable, large brick with its' plastic-barreled, extremely short focus-throw DX Nikkor lenses just wasn't for me.