I was able to get from level 30-40 in two solid days of playing time. How? Scarlet Monastery!
SCM is geared for levels 30-40 because all the elites are those levels. The highest I believe is level boss there is level 42. Anyways the runs arent that long (maybe and hour and a half max... atleast in my case) and if you can dedicate a good solid day or two of playing there, you can get great gear and level up a good amount. In my case i did each run untill the next one was best for my level (obviously) and each run ran me up a good 3-5 bars exp depending on my level. This was all pre 2.3 so I guess you could do it faster now.
TIP: If you need to repair your gear, then I recommend just heathing and leaving at least two people behind to summon you back. Then those two people can do the same. By the end of the run your hearth will be able to be cast again, if you really need too.