Not much difference.
Between the 335 and 295 cc style 410 implants, you are talking about 3 mm of difference in projection and 5 mm difference in width of the implant. In other words, you are looking at about 1/10th of an inch out and 1/5th of an inch around. You should not worry too much about the difference in these sizes. Depending on your chest width, I would probably use the larger implant if you are worried about one not being big enough -- I doubt you will think the 335 is too large.