When giving advice about implant sizes there is a lot more information needed. It would help to also know your height, weight, starting bra size, and current size of your implants. A 300cc implant is going to leek very different on a patient who is 5 feet tall and 100 lbs, versus a patient who is 5'7" and 160 lbs.You could try and experiment at home by adding 1/4 cup of rice is a loose baggie and using this as an insert into your bra, and this translates into about 60 cc of implant volume. Your surgeon might also have sizers in the office you can try.Because the volume change your surgeon is recommending is modest, it makes me think he feels your implant size is appropriate for your frame, and that a big jump in size may be a mistake. If you are small framed, 50-75cc may be a fairly significant jump for you. It has been my experience that patients who feel too large after their augmentations are some of the most unhappy patients I have seen. If you want to go slightly larger, you may be able to achieve that look with a bra. If you would rather have surgery ask your surgeon what their concerns are with you going larger. There is a saying in plastic surgery that "the enemy of good is perfect". If you have a great result, and it is still worth it for you to go larger, ask your surgeon if this is a simple or complex procedure and if he feels the benefits outweigh the risks.Best of luck to you!