I'm one of those people who leveled all my classes to 50 in the semi-drought leading up to HW.

I take Coerthas 30-40/42 (depending on if I'm in a good and fast group), then Northern Thanalan 40-50.

In my experience, mileage may vary etc., I would get one level per hour for those twenty levels. Allowing time for food, sleep, bathroom and life, that meant finishing a class or two every week. Some I found more boring than others, so naturally those took longer because I just couldn't be bothered.

Right now there is a situation I'm not sure the OP is considering. EVERYONE that has a max level character is gearing up for or already running VA and Diadem. That will be the case for the next couple of weeks. Then things will cool down again, alts will get picked up, and the fate trains start choo-chooing once more. Right now is a very bad time to try to do fates, at least if you insist on having a group for them.