About 3 months ago I swapped systems from a Pentax K-7 to a Nikon D300s. I have pretty much replaced my Pentax lenses with Nikon equivalents. I was writing up a report on my comparison of the K-7 and the Nikon D300s, saved on a flash drive, which I have now lost! I won't bother doing all that again as I'm not a fast typist. Suffice to say I'm happy with the results, though still getting use to the "Nikonthink" way of menus and doing things, not as good as Pentax imo.
However results-wise, and this is entirely relating to sport-shooting and all of this should be read in that context, I'm very happy. I'm getting lots more keepers, and am actually not bothering to keep some shots that I otherwise would have with the K-7 because I get so many other good shots. This is all down to the focusing and tracking ability of the D300s, purely and simply.
With the K-7 I was using the Sigma 70-200/f2.8 (screw drive) usually coupled with the Sigma EX 1.4x TC. With the D300s I'm using the Nikkor 70-200/f2.8, usually coupled with the 1.4x TC, but also the 1.7x TC. This Nikon lens uses Nikon's SWM in-lens motor for focus. It's very fast(and silent, which I'm still getting use to!). In good weather the 1.7x TC hardly slows the lens down at all, in bad weather, well it's too dark to use it anyway as it steals 1.5 stops of light!
If I wasn't quite so into shooting sport, I'd still be very happy with my K-7.
Things I miss from the K-7:
- Size and weight.
- Pentax saying it's weather-proof, Nikon seem reluctant to commit to this.
- The better utilisation of auto-ISO, the Nikon way is not as sensible.
- TAv mode - while this can be done on the D300s, it's not a mode, it's manual mode with auto-ISO. To me, if you're in manual you should be the one controlling the exposure, auto-nothing.
- Shake reduction with the primes I've got (35mm and 50mm).
- Being the only one sideline with a Pentax! I usually cheer for the underdog.
- The focus assist light wasn't as bright as the D300s (which is a good thing), and it didn't come on so readily, the D300s one comes on even when the camera can easily focus, so I've had to turn it off.
- The quiet shutter.
- Consumer grade weather-resistant lenses.
Things I prefer about the D300s:
- The AF button, which I always use, is in a much more sensible and comfortable position than the K-7.
- Focus speed and tracking. Even with the 1.4x and 1.7x TC on I can still shoot rugby.
- Availability of lenses and peripherals. I picked up a 2nd-hand 1.7x TC straight away, of course it's fully compatible with SWM focusing. They have a choice of 50mm lenses!
- VR is pretty cool when you see the result through the viewfinder.
- The TCs correctly alter the aperture and focal length in the viewfinder and exif.
- Having programmable buttons is good, but then I never felt the need with the K-7 as it was easier to change things.
- Having a "My menu" giving quick access to commonly changed settings.
I haven't used the flash much yet on the Nikon so can't comment on that, though so far, so good. Their latest flash actually ships with a sto-fen like diffuser and gels, which is nice.