My tuppence worth, albeit from a Nikon user; if you don't have to carry your kit too far, go for primes every time. Personally, I'm not going to be overly impressed with having to carry too much over a 30 mile hike & a few thousand feet of ascent, so sometimes a zoom or two will just have to do. My 18-35 & 24-85 ED zooms cover just about everything I might need, and with a D700 represent a reasonably light compromise. Half a dozen Nikon primes might mean not getting the shot at all, but I suppose it would at least be a sharper empty space on a memory card ...