Fire, Walk With Me

Through the darkness of future past,
The magician longs to see
Once chants out between two worlds:
Fire, walk with me!

Twin Peaks: Fire Walk with Me

Easy way to do this is taking priest and mage with you. You take the flag, priest shields you, you run straight to speed boots out of the flagroom. BE SURE that you took the boots 'cause sometimes you should stay for 1-2 sec to take it. Mage must use slow fall on you (levitate is good enough too but can be canceled by any damage so I prefer mage's); after this you must run directly to the cliff and jump down before speed boots would fade from you. Thus you will have +100% speed while falling :)
After landing use Swiftness potion. Priest/mage should assist you ofc with novas/sheep/fear/dispel/speed-shield/grip/etc. +Speed boots enchant or meta gem recommended too. Hunter's aura good sometimes, but will daze you with any damage, so be careful with it. I capped the flag in 59 seconds as mage (blink ftw) with priest assisting me.

There is one more way to do this achievement (horde only) -- it is easiest and really funny :D
You should find some alliance faction elemental shaman (hardest part) and take a mage with you. Again, take a flag, take the boots, have slow fall (not the levitate) buffed on you and run to the cliff. Shaman must already wait you on the cliff. Run directly through shaman's model and try to "target" yourself to the gates of horde base. Thunderstorm... and you flying away with 300% bonus speed :D You will land not so far from the horde base :D

Good luck for everyone!