Random is going to random. The simple fact is, if you're below 100%, you WILL eventually fail. And just like if you keep trying 1%, you will EVENTUALLY win.
Is either case worth it for you? Hell no. Just stick to 100%.
And if you want your answer, go dig it up from DMM patch notes. I'd like to know myself, but I certainly am not bothering to dig it up.I wouldn't recommend Thunder unless you have Kirin and/or Thunder Aphro...
Anyway, if you don't want Phantom Lord Thor, Raiko or Marduk would probably be good for you. Raiko's Awakening is really far away, Marduk is in a few days or a week. But again, I wouldn't recommend Thunder without Kiron or Thunder Aphro.