I think you're right to go to 6 prongs for security. It's definitely more secure. My first e-ring is 6 prongs. with my anniversary ring (a solitaire) I went to 4. But the way the jeweller explained it to me was this--if security is the only consideration, 6 is better than 4. With 6 if you have a problem with one prong, 5 more will hold it in--but with 4, only 3 prongs, which isn't enough to hold a diamond in. HOWEVER, its not necessarily true that you will definitely run into a situation where a prong will bend--in fact, unlikely if you regularly clean and check and the setting is well made. And there are other considerations such more light hitting the stone, whether you like the stone to look rounder or more squarish (I think 4 is more popular now partly because squarer stones are in vogue), so 6 is not right for everybody.
My big question is: Is the ring insured? Against everything (including stone loss or damage?) While most of us would hate to lose the diamond from our original e-ring, think how much worse if the unlikely happened--and you weren't insured to ever get anything else. This did happen to my mother, so its possible.