Will change in diameter of implant to go bigger make my breast look even wider?

Getting a wider diameter implant will make the breasts wider. You can't have it both ways it will be water on the side and water toward the cleavage. You must make a decision of what is most important to you, bigger breasts or wider breasts.

You are only going slightly wider with the larger implants that you mentioned.  Chances are the differential in volume from 380cc to 505cc will add a lot more projection to the breasts which will make them stand off your chest wall more.

Because you already have implants, your pocket (capsule) is well-developed. When surgeons put new implants in, they usually cut the capsule towards the middle of the chest to move the implants closer together. This is because the implants always have a tendency to settle to the sides. If your surgeon makes room for the bigger implant by cutting toward the outside of the capsule (toward your arms), then your implants shouldn't look much closer than they are now, especially because your new implant width is only slightly wider than your current one. An in person exam might help confirm this, but even then, surgical results are never 100% predictable.