For me, there's one Pentax feature that no one else has (please correct me if I'm wrong) is "TAv" setting exposure. I believe the "program setting" on the Nikon is similar to the the older "program setting" on the old Canon EA1 (from the 1980's) in that if you adjust the aperture, the shutter speed is moved in the opposite direction. Since to me creative control is always focused on shutter and aperture, TAv mode automatically adjusts the ISO. To me it's a dream setup for any kind of action (and use the back focus button and you'll be able to zoom in on a subject on a stage, use spot focus and with the front and rear dials just concentrate on the composition and DOF). In that case I think you'll have your expert friends contemplating a switch.
So in a nutshell, investigate the handling very closely, that's what will really make the difference.
The downside might be to consider video capabilities. I think the difference isn't too great, at least between the Pentax and Nikon "C" cameras (Canons usually comes out on tops from reviews I have read). But I didn't get my K3 for video (there's plenty of parents who do that at my kid's events). To me some video is just enough.
Oh, yea. One more thing: Internal stabilization vs external: besides saving money on lenses, knowing that any lens that gets attached to the Pentax (at least for me) was a great plus (another thing that I think the conikon crowd might get jealous with). And as far as that goes, from the review on the image quality of the K3, the following was written up (see:
Review: Pentax K-3 - General Image Quality | PentaxForums.com Reviews. The point is:
Quote: Users with steady hands will be able to get sharp hand-helds at shutter speeds as slow as 1/8s with normal lenses. This degree of stabilization combined with the K-3's solid low-light performance makes it an excellent nighttime shooter overall!