Invading blighttown... You are one sick bastard
40 might be a bit high for blighttown and Sen's... Try 30. http://mugenmonkey.com/darksouls/?c=3501863214124630
And yeah, if you wanted you could go fight 4 kings right after you finish the undead burg. I'd recommend ringing the second bell and then rushing for the chaos ember first though, and to do that you need to get through sen's fortress at least, and get the flameplate ring.
Lightning weapons will help IMMENSELY when going down to Lost Izalith for the flame ember, so I recommend upgrading a battleaxe to +3 lightning and then heading down there right after Anor Londo. That way you can get the chaos and fire ember in one go. A +5 lightning battleaxe with a +5 heavy body piece of some sort will also make the Four Kings easy-sauce. This is how I got through them on SL 1, so on an SL 30 you'd have no problem.
To get the chaos ember, you'll need to equip full gold-hemmed set, the flame stoneplate ring, and flash sweat. Pick off the taurus demons, cast flash sweat, run for the ember and grab it.