I think you are right at the line between 340 and 400. You shoot a fast bow and your tips and broadhead are heavier than average at 125g so in my personal opinion, I think you'll be just fine at 340.
This opens up the option to cut longer arrows or even run heavier inserts and/or tips/broadheads.
If I recall correctly, your draw length runs from the string to the edge of the arrow shelf at full draw. I would start off cutting your arrows 2" longer than your draw length (so 28.5") and see how they shoot.
With a 340 spine, I doubt you will see any shaft whip when it leaves your bow.