Wow, I have been neglecting this blog for a while it seems. First news, I'm now level 70 and taking a break from 5-boxing to do some PvP. Eventually I will go back and 2-box my warlock (with Paladin heal-bot) from 30-60 and then 5-box the remaining classes from 60-70 but that probably won't be for some time.
After Ramparts I moved on to Hellfire Blood Furnace which went surprisingly smooth. After Blood Furnace I went to Coilfang Slave Pens where I started to run into trouble. While I have to give a kudos to Blizzard for making instances more then just tank'n'spank, they don't do well for a 5-boxer. :/ After Slave Pens I went on to Underbog which posed even more trouble with fears, AoEs, etc. Around that time I decided to try and clear out a few zones worth of quests, including collections, which didn't go too bad but the xp/minute was still fairly low overall. At around level 67 I went into Mana Tombs, after capping the Terrokar towers, and farmed Spirit Shards from the first boss up to level 70. I ended with the PvP Helmet, the PvP Meta Gem in it and the Epic PvP ring.
Now that I'm 70 I'm not really 5-boxing anymore since my only goal with 5-boxing was to get 5 classes to 70. It took me under 18 days played to do 1-70 5-box which I'm happy with since it likely would have taken 50-100 days played to get 5 level 70s one at a time.
As mentioned earlier, I think I will use my level 70 Paladin to follow my level 30 warlock around until he hits 70. Once there I will likely level on rest XP alone my other 5 characters, most likely just farming trash from Outland instances or doing quests that yield good rewards.
My quest to level 5 World of Warcraft characters at the same time.