Struggling With Implant Size Decision - 340 Demi VS 400 Full profile?

I am scheduled for breast augmentation in six days and I am struggling with implant size. I have been offered Motiva Ergonomix implants: 340cc Demi or 400cc Full profile. My breast width is 14cm and my surgeon estimates about 1cm of breast tissue on each side, meaning a 12cm implant should fit my frame. I will be having a dual plane (half under / half over) procedure. About me: age 29, height 5 foot 10.5, weight 67.8kg, clothing size AU 10. I do not usually wear bras but estimate band 34 and cup A. My goals: I want to be in proportion with my body and look natural, with a soft slope and healthy fullness. I do not want obviously augmented breasts. My biggest fear is a round, “ball-like” appearance. I want a nice shape and a happy medium, not too big and not too small. My surgeon strongly recommends 340cc, however previous surgeons advised me to consider 400–420cc, which makes me second guess going smaller. My questions: Based on my height, weight, and frame, which size would you personally lean toward and why? How noticeable is the real-world difference between 340cc and 400cc on someone my size? Is it possible to very roughly estimate what bra size each might result in, understanding it is not exact? I know you cannot assess without seeing me in person, but I would really appreciate professional guidance as I am feeling anxious about choosing correctly. Thank you.