HOLY jesus, Lv.70 and only just beating sens?
I'm usually Lv.70 or so at the last boss or in NG+

Regardless, I totally forgot about the flamberge. I'll definitely have to use that on this character as welll~
You could go lightning, fire, or chaos if you want. Hell, you could even go +15 and buff it.
I'd recommend the last option personally, gives you more options to work with, and you don't have to worry abut elemental resistances. (Unless for some reason the flamberge cannot be buffed... but I doubt that)