Only using Soaring Blades, you want to go Break Stance with Break Stance D Bonus. Here is how the multipliers break down:
- Elemental Stance + Up matching element: 132%
- Elemental Stance not matching element: 115%
- Break Stance + Up on breakable part: 148.5%
- Break Stance on non-breakable part: 100%
- Break Stance + Break Stance D Bonus on non-breakable part: 131.5%
As you can see, (not counting the natural element matching bonus) Break Stance + BSDB will give you overall more consistency and higher potential damage, and it also means you only need one pair of Soaring Blades (preferably Light element) instead of needing to get a full rainbow set.