Is 25CC going to make a big difference in breast size, like will that make me go up a whole size?

Thanks for your inquiry,  first bra sizes are not standardized.  Next cup size really refers to the amount of projection-how far the breast sticks out.  A 400 cc ultra high profile implant has 5.4 cm of projection will a 425 cc moderate classic has only 3.4 cm of projection,  2 cm less!  Without knowing the particulars of your goals it is hard to advise, please ask your surgeon and best of luck.  

If you're considering another operation for the sole purpose of increasing the volume of your breasts it would be very unwise to add 25 mL. There would be an almost imperceptible difference.