Oh, it was plenty challenging, with most of my attempts ending within the first few levels; this time, I got a lucky break. :)
For the first 18 levels, I just went straight for the stairs. I wanted to make sure that each time I killed something, it was the first time, (since they only give you experience the first time you kill them) so I made sure to do a minimum of back-tracking. Around the time I was at dungeon level 18, I was tough enough and well established enough to start clearing out floors. Well, I never really *actually* completely cleared any of them out, (with a few exceptions) but I made sure to kill everything at least once for the experience and if anything revived before I got to the staircase, I didn't let it bother me. I tended to leave Arch-Viles for last when fighting packs of monsters so I could pad my kill count a bit with re-kills, but other than that, I didn't put any effort into padding it.
At the beginning, I burned through health and armour like crazy, but was lucky enough to find enough to keep me going. For a good, long stretch of the mid-game, I was juggling between two power-modded red armours and repairing them whenever possible and that helped me build up a stockpile of med packs and after that, the lowest I ever got on med packs was six. I was hoping for an Onyx mod, which I was planning to slap on one of the red armours, but around the time I finally found it, (in the late thirties? I think?) I had Phaseshift armour, and after giving all due consideration, I decided to put the Onyx mod on the Phaseshift instead, my reasoning being that I had Badass trait to mitigate the knockback increase, and since I was zooming around pretty fast, thanks to HR 2 and Tac boots, melee protection was more important than fire protection. I slightly regretted that choice on some levels when fighting numerous fire enemies, like Revenants and Mancubi, but overall, it worked out quite well. I built a Tactical armour early on for no other reason except that it's one of the few assemblies that Arron's rules allow, but I ditched it shortly afterward because it was taking too much damage to be useful. I think it's an assembly which is much better suited to ranged weapon games.
I reached character level 25 around the early eighties, which made the last twenty levels a little more tedious, since I no longer had any goal to shoot for and I was already well over the required 85% kills, but I plowed on anyway and eventually did it. Yay! :D