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.
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.