4-5m win (depending on misses) with RNG/NIN + RDM. RDM gravities, RNG shoots with crossbow + holy bolts until it's dead. Can't get any easier. I don't use any level appropriate gear either, so as long as you have RNG over 60, you can easily adopt this strategy. RDM is my mule so I don't even nuke with him, but you could kill it even faster if you did.
I know you're looking for BST strategy, but the best strategies certainly don't involve BST. Way too slow and inefficient.