For a super hard challenge, maybe try one of the total conversions that removes all leveled things: http://www.dreamingthepyramid.net/TNR-TIE.html – that’s been one I’ve been meaning to try if I could work up the energy to dig back into mods.
You want hard? Try the “wanted man” thing. Build up a bounty and never pay it off! Kill every soldier you meet! I heard a rumor that there were a handful of NPCs that would give you missions/sell buy from if you tried to keep it up.
There’s not actually any special high infamy/bounty things in the game, other than a few doomstones. If you get your infamy and personality high enough bandits and the like will stop attacking you though, and you can talk to them about rumors, but it’s only amusing the first time.