It appears that you like the Nikon D700, so why not just get a D700? If you're going to shoot sports/action, the D700 can shoot 8 fps with a battery grip, and the the 51 point auto-focus system is better than the 5D MarkII for action.
Take a look at the photos in the link below....this photographer takes some impressive action photos with the Nikon D700 and 28-300mm lens combo:http://www.flickr.com/photos/mingthein/5166294336/#in/photostream/
Personally, I'm just an amateur and I don't have a brand loyalty to either Canon or Nikon...you can see in my signature that I currently own the 5D MarkIII, but I've owned both the Nikon D800 and D700. If I was on a budget to get an all around great full frame camera, that can be used for both landscape and action photography, then I would probably purchase a used Nikon D700 with a battery grip, along with the Nikon 24-120mm f/4, or the Nikon 28-300mm, and the Nikon AF-S 50mm f/1.8 ($200) for low light. You should be able to get all of this equipment for around $2,500.