I am switching from a 350cc saline to a 500cc gel implant, will there be any difference in size?

By definition, the volume of your breasts will be 150 cc larger when going from 350 to 500 cc's. What is interesting and sometimes frustrating is that this does not always change cup size in predictable ways, or produce a look that is noticeable. For most women, more than 100 cc's is enough to make a difference.

Based on your stated plan, your breast size should increase. However, you are wise in considering the different “look” that can be achieved with saline versus silicone gel breast implants. Best to select your plastic surgeon carefully. An experienced board-certified plastic surgeon will be able to guide you when it comes to the different look/feel that may result from the use of different types of breast implants. Best wishes.

Unfortunately,
you have not told us your bra size just your cup size. If you are a 32 or 34 each 100 cc’s of
implant corresponds to 1 cup size change.
If you are a 36 or 38 each 200 cc’s of implant corresponds to 1 cup size
change. From this, you can compute the
volume required to achieve your desired goal.
I always recommend small round textured silicone gel implants placed
retro-pectoral since they look and feel more natural, are more stable, less
likely to ripple or have complications needing revision. Implant profile is irrelevant in the
retro-pectoral position since the muscle compresses it. Best Wishes,Gary Horndeski, M.D.