I currently use a ~35' (~10m) fiberglass telescoping mast, and I love it. It's great when I hoist my 10m window line j-pole (thank you KB9VBR!) and now that I'm messing around on 20m, it's just too short. My SWR is a bit higher than it ought to be on account of ground reflection since I can't get the base of the radiating element more than about ~1m (~3') off the ground.
The antenna I use (currently, at least) is fairly lightweight, so I'm not worried about mast flexion since the wight will largely be just outside mast center.
I am not to deterred by cost, and I am trying to avoid metallic antennas for fear it will mess with my radiation patterns and SWR in a new way. I am greatly interested in telescoping options.
Are you familiar with fiberglass or carbon fiber masts which get the top to a definite 15m (~50')?
Nearly all of my operations are /P, so it really has to be fairly convenient. I recognize that these requirements may be a little mutually exclusive.
I haven't used telescoping fiberglass, but I'm planning to build a PVC mast with schedule 80. 1/2" fits inside 1" fits inside 1 1/2" fits inside 2". Couplers and reduces to assemble it into a pole, guy wires and a base with sand bags to keep it vertical. Using two sets of 10' sticks would give you 80' height.
You could also look at the Buddipole which claims to work 40 m - 2 m with different coils.
PVC doesn't really work well for a mast above 20 feet or so. Pipe couplers are not strong enough to join the sections, there needs to be a foot or more of overlap.