My biggest lens is a 100-400, so I bought the 2531 based on price and weight even though Gitzo recommends the 3-series for 400mm+. The issue isn't the weight the 2531 can support -- it's plenty sturdy enough -- it's vibration damping. I found it pretty good natively for long tele, but was never satisfied with the center column so I replaced it with a Markins TB-21 base (https://www.markinsamerica.com/MA5/TB-21.php
) and that noticeably improves stability without adding weight or bulk. That does bring the price closer to the 3531, but it is still a whole lot lighter. Getting a 2-series systematic without the center column would be something else to consider. Anyway, I put a Markins Q10 on that rig and that's a very solid set-up that's easy to tote along.
The 2531 + Markins Q3 + TB-21 + spikes and leg wraps was marketed by the Nikonians user group (sorry) as the "MAGICA-2" tripod set (3531 + Q20 + TB-30 + spikes is the MAGICA-3), and backed that up with engineering reports on vibration damping. You can Google "MAGICA Tripod" to learn about those packages. Not sure I buy the objectivity of those reports, but they are an interesting read.
Anyway, I think the 2-series Gitzo tripods are a great option, particularly when you catch a rebate or sale.