Thanks for all the input folks.
In the end I decided to go for a used D3 (23,000 shots) and managed to pick up a barely used 24 - 85 AF to get me started. Image is the second shot straight out of the box at iso 6400, why did I kid myself the Pentax could hold itself up with the big boys!
Just found this thread. Guess it's too late.
FWIW, I wouldn't swap my D700 for anything. Except for the impossible: another, simplified
Nikon with a real
pentaprism and screens designed for non-af lenses; a Hassy 500 series with an FF sensor (but I couldn't buy that even if it were available).
The D700 allows me to shoot in any light I have ever wanted to use. I still have a D200 but it never gets used. Night and day. All my lenses are non-af prime AIS Nikkors: 2.8/24mm; 2/35mm; 1.8/50mm; 2.8/105 Micro; 2.8/135mm; 2.8/180mm (the only af one - couldn't get an af one at the time); 8/500 Reflex.
The reason for the af 180mm is that I'd bought a brand-new 2.8/24mm-70mm G Nikkor, and I couldn't get rid of it fast enough; a terrible lens. The dealer would only accept it back if I bought something else, hence the 180mm. I shall never buy another zoom - it was my first and only such Nikon aberration since I started in this game.
You can pick up great used Nikon/Nkkors from Grays of Westminster (London) and they are great specialists with whom to deal.