It must be noted that there are constraints. Not all frames are designed to accommodate the latest generation of ultra-long droppers. Mountain bike designers have become cognisant of the grown-in dropper post length and the demand for them among riders, but older frames could limit your insertion depth and ultimately cap the ability of dropper post travel you can use.
Dropper post length and insertion depths is not the only consideration when choosing the best dropper post for your bike, seat tube diameter and potential cable routing must also be considered to assure fitting compatibility.