I did that challenge but the highest level I reached was 72 before to move to a new game's release. For the Vanilla part the most dangerous zone, most avoided it, is: Eastern Plaguelands, I lost a few level ~45 there.
I'm not going to do it yet here but I thought about it a few days ago hence my surprise when I saw this topic.
For those who wonder what that challenge is, check the rules:
Iron Man Challenge Rules.
Note that we, normally, didn't choice the race, class and used a random character generator tool. Rogues and Priest were hard and the easiest was Night Elf druids and hunters.
That challenge is the top school to learn definitely how to play in the matter of strat and positioning for the pulls. An unforgettable experience and a major improvement of the behavior and awareness of the game world surroundings. One will never play any MMORPGs the same after that.