When you're pricing connectors, be sure to check out Phoenix Enterprises - http://www.phoenixent.com/ . I use their S100 connectors and also their double-wipe DIP sockets. I think machined-pin sockets are way over-rated for applications where high numbers of insertion cycles are not anticipated when compared to _quality_ double-wipe sockets like those from Phoenix.
Also, I'm not sure what thickness material Ant is using for his backplane, but the N8VEM backplanes are twice the thickness of the component cards to provide rigidity and reliability. This needs to be taken in consideration when ordering connectors, since you'll need a slightly longer tail to ensure full penetration of the board.
Best,
Jack