A lot of people think of a monopod as a single, vertical leg. Instead a monopod is more stable if it is used with the leg at an angle - like a tripod leg. Your legs provide the other two "legs" of stability. If you are holding the tripod in a vertical position, it's not very stable, but extended in front of you to a 60-70 degree angle, it's very sturdy. Using it at an angle also makes it a lot easier to adjust the height. Taking a short step back is all it takes to lower the level of the camera.
Which monopod to buy? This FAQ may help.
www.nikonians.org
I mention all this because B&H carries six Gitzo monopods - a light Traveler, a Series 2, and four Series 4 models for long lenses. The Series 4 models are 3 Section, 4 Section, 5 Section Long, and 6 Section models. Among these monopods, the extended height is 60-64 inches on all of them except the 5 Section Long model. This means the thinnest leg section is fully extended for a height of 5 feet 4 inches on most monopods. The 5 section Long model extends to a height of 74 inches. That's the only one you could hold at a 60 degree angle with the tripod extended in front of you for stability. So in my view, this one is the only real choice:
This one - the Gitzo GM4552L - is a "5 Section" monopod and it's almost 12 inches longer than the others when fully extended. That also allows you to minimally extend the smallest leg section or have enough length for uneven terrain. It's 6 ounces heavier than the 2 Series model, but sturdy enough for any long lens and camera.
My only complaint with the 5 section Long model is that like all Gitzo monopods, it has a round rubber foot rather than a spike or teardrop shaped foot. The round foot is fine for paved surfaces or indoors, but is not as good for rocky, uneven ground or other outdoor surfaces.
Here is the ProMediaGear 4 series Long monopod (81 inches) - and it does have a teardrop foot that is convertible to a spike. It includes a monopod head. The downside is that it is 3 ounces heavier and a little longer closed.
Back to your original problem.