As for the 3.5 Monk thing, it was just a passing comment from my vague recollections of a monk completely breaking a campaign I played in, but there may have been some third party fuckery or some phenomenal stats involved. I do remember the DM for that campaign enjoyed snapping rulesets over his knee (he was an appalling min-maxer as a player) so he may have houseruled the monk into superpower because he was a weeb. Like I said, it's been over a decade.
For my campaign, I've narrowed it down to Pathfinder or 5e. The core rulebooks for 3.5 are too hard to find and most of my player pool (students from local universities) aren't likely to have rulebooks or know the ruleset well enough not to need them.
I've run low-magic, survival-type campaigns in 3.5 with success before. I didn't find the system too easy for the players and so long as you don't hand out too many baubles as a DM you can keep things competitive without the players feeling under-rewarded. It's all about managing expectations. When you're in a Mad Max wasteland, what would be a boring item or encounter in a normal campaign is an amazing find. I had two players actually brawl for the right to have a masterwork longsword, and an encounter with an Ankheg was a cause for wild excitement at the thought of stripping its corpse for its blood and exoskeleton - it wasn't just a monster, it was a resource. Limiting arcane casters to sorcerors only worked well. The sorc is a much more focused caster with a narrower but more potent spell pool, and is slightly better in a fight where they can't cast. I didn't get any caster supremacy issues in that campaign either.
It still strikes me that 5e PCs are much harder to kill than 3.5e PCs unless you start introducing houserules. Once they hit 8th level or so they're almost indestructible, whereas even at that level 3e PCs were vulnerable to all sorts of things. I'll see if PF is any better, or if using an alternative encounter table/formula for 5e restores the balance a bit, as all accounts say that the default one is too much of a walkover for the PCs 90% of the time.