In Reddit got this answer to Ace & Holy Rod + Draco Spike discussion:
Draco Spike stacks. It is best to just run 2 of them and spam Tri-Beam. I tested it out on the white dragon.
966 Mag with no Draco Spikes: 126k, 133k, 134k
938 Mag 1 Draco Spike: 188k, 190k, 215k
910 Mag 2 Draco Spikes: 262k, 271k 274k