Others have done it faster, but my personal best was a neutral human air/offense shifter who hero'd in 75 hours with all controls in the 90s (i.e. I spammed a lot). Mostly it depends on finding good groups, which usually requires having a good tank. A "mediocre" tank can often be turned into a "good" tank by the addition of a support class (healer,arcane,bard) but then you're missing out on damage you could have had if the support class were replaced by a damage class.

Shield spec paladins are about the best people to rank with, since they avoid blows very well, have build in dam reduction, can heal themselves and can do damage during combat. Some people prefer LG conjurers but I dislike having to wait for conjuring.

Another big factor is finding a competant group leader. Someone who knows the layout of the area where you're ranking will generally be quicker about getting you from one mob to the next. To this end, if you group with someone who seems competant then by all means try to group with them again if possible. This also allows you to build IC alliances that can help out later down the road.

And finally - don't mob die. This is important. The fastest anyone is likely to gain xp over the entire life of a character is around 10k/hr. A more realistic figure would be 6k/hr. I'm including time spent finding a group, role-playing, etc. So if you die when you're in the 40s then you're looking at a 15-20k xp penalty, which translates to an extra 2-3 hours before you reach 51.