User blog comment:Miskos3/Fairy Tail Chapter 385: The Celestial King vs. the Underworld King, Review/@comment-24734283-20140523231005/@comment-7418318-20140525084112

I don't remember where exactly it was, but at some point either Lucy or someone else mentioned how Loke drew a lot of power.

Then there's also the figth against Bickslow. Before that we've seen her summon more than just two Spirits without getting exhausted, but in the Bickslow fight, she was drained from summoning only Saggitarius and having Loke summon himself.

While that's not enough to proof it for sure, it does strongly hint at Loke draining more magic power than even other Zodiacs. At least I think it does.