Would not recommend the wiki-recommended level and upgrade for Catacombs of Carthus. I'd actually recommend being lower on the range rather than say, lvl 49 with a +4 weapon. With a +10-capable weapon (i.e. not something that maxes out at +5, which count as double their normal value) at +4, I could find but ONE person to summon and he was inexperienced and got himself killed immediately. I'd aim for a lower level for that place or higher, possibly. On my other characters, I was usually at a different range and found people, though to be fair, the catacombs suck. People just don't want to coop there. It was a good range for the boss, though, fortunately. Two summons were there without effort.