Gitzo uses pressure cast magnesium parts, but "cast" isn't necessarily inferior to CNC'd.
For long lenses/wildlife you have two good choices for a head... either a gimbal or a pan-tilt. Gimbals are the most commonly preferred, but at the high end (true) fluid pan tilt heads are often preferred. I've run the gamut from pan-tilts/fluid heads to Gimbal heads, and I'm back to using pan-tilts (UniqBall). A ballhead is a very poor choice for a lens which needs to be rapidly repositioned (although there are ballheads which convert to pan tilt).
The tripod choice depends on how it's going to be used... if you are going to be using it with a gimbal head that is (affectively) unlocked and the camera/lens in motion, then you really only need something that can support the weight without failing. The more resistance you are likely to use (locked head/friction) the more rigidity/vibration absorption you need with a minimum recommendation being a useful load capacity 2x your max.
I would also recommend a tripod that extends to a height higher than you intend to use it at. This allows adaptation to uneven terrain while maintaining the required height. But more importantly it allows you to not extend all of the leg sections to the max which greatly increases stability.