I've done 20.

Last night, I managed to do 17 hit of quickening, 16 hit of quickening, 16 hit of quickening to (SPOILER)Ring Wyrm, ending his life!
*Keep casting Charge* *Release another series of Quickening*
My normal quickening hit is 10.

About the Quickening damage, it doesn't matter, you can use anyone as long as you chain it high enough (My Fran and Basch appeared a lot).