I always find someway inappropriate to start thread about the fact of switching brand in any specific brand photography Forum. Switching is one of those personal choices that many of us made and will make but depends on personal need, aims, way of shooting, professional use and so on. The experience, by the way , it's shareble. At least this is my opinion. But I don't find the OP post offensive. My experience:
1 - I have got nIkon d300 and nikon d7100. In any way I consider those camera better in IQ than pentax counterparts. Nikon's RAW are "anemic" , but the quality is here both in Penta and Nikon, for sure.
2 - AF module (Multicam DX 3500) is really good for sports photography due to wide span of the AF points, f/8 compatibility (TC Use) , 51 AF points, 3 d tracking . But for stills itìs way too much. For stills my k5 has a sufficient AF, the performance in newest AF modules with appropriate firmware for sure is better.
3 - I'm saving money for K1 for general photography. I will never go FF to 36/42 mpx with Nikon (D800 camera has too much microblur due to the mirror mechanism). D600/D750 (24 mox) are plagued with problems (shutter mechanism, oil on the sensor, green magenta color cast).
4 - Nikon CLS (creative lightning system) is amazing. my SB 700 (used item, 190 Euro in brand new conditions) simply flashes PERFECTLY every shot on and off camera, wiressly remoted (by camera features, 3 channes).
5 - I MISS SR . Nikon's Vr is not the same.
6 - In Italy Nikon's used market is strong. Pentax simply has no market , unfortunately. Pentax lenses (in Italy) are much more expensive.
7 . Yes Nikon already have the 1.4 and 1.8 and 2.8 prime ens line ups...........but.........how many of those lenses will be in my bag?
To sum up my opinion, for the OP: don't bash your Pentax gear, keep it with you and use it for its strenghts and amazing IQ.
Good light!