I can tell that from my experience, the first 10 seconds of the Capra Demon fight are one of the hardest of the whole game. The two dogs really are bitches.
Quelaag is hard too. On my walkthrough I killed the boss in the Catacombs, the hydra and Sif before even meeting her for the first time, yet I had some troubles.
It's also quite remarkable the game is so unlinear there are like 3 points where the story converges, but all the things you have to do between these moments are completely free to do in any order.
Since I know the game now, at least getting to Gwenevere shouldn't be that hard.
Havel armor / +5 Tomb lord sword combo ftw. With the right rings and build I could use those without penalty at level 70. Those little light pvp roll-happy my old friends will suffer again.
PS : thumbs up for 600 renown / 200 infamy