Instead of worrying which of these two choices is better, you should be asking if EITHER of these will achieve a 2 cup-size increase! (Because I don't think they will.)
Generally, it takes about 250cc to equal one bra cup size for your height, weight, and bra size, so you wil be adding about 1 1/2 cups to your present bra size--falling short of your goal size, and possible leading to the number one reason for re-operation after breast augmentation: new (larger) implants. And this costs about $3500 or more, depending on whether or not your surgeon charges a surgeon's fee for re-operations!
If these are your only choices, the answer is easy: 400cc.
But if you were my patient, I'd ask you to try on implants in a bra and stretchy top and not look at the numbers on the implants (because if you chose a 400cc implant, I would use 450-500cc in your body UNDER the muscle). Below the muscle has a much lower incidence of capsular contracture, less visibility of edges or ripples (even in silicone implants), a softer, more natural result, and quite low risk of activation distortion if fibers are properly released inferomedially and laterally. Less chance of an unsatisfactory complication and need for re-operation, and higher likelihood for the desired aesthetic result! Please do more research! Click on the link below. Best wishes!