To me, it dosen't matter when I get the skills I need for my build as long as it's ready by lvl 80. What I'm doing is not farming anything until lvl 70. Then I will increase my gap by 1 until 9 gap at lvl 80. At this point, you shouldn't worry about lvling as much so you should have more fun grinding SP. An occasional 1 gap is to keep the masteries and some new skills coming as my lvls progress without a sufficient amount of SP needed until lvl 70.
Note: The 9 lvl gap until lvl 80 will rake in 283 thousand SP! No lie!
SP Calculator <--- Use this to calculate.
All this is your opinion but that's the fastest way to lvl and get a nice amount of SP. Even if you keep that 9 gap at lvl 80 you can rake in more SP. This may be slower than low lvl farming but it sure as hell makes you enjoy the game more.