I'd go with opal for both pve and pvp.. About chance for lv 5, I think it's 10% chance to go from lv 4 to lv 5, but not sure..
Takanodan, you would have a link which shows the chance of each lvl or experiment conducted? I tested it with 100 box aquamarine and got only one lvl 4
I don't know of any experiment.. I said I think might be 10% 'cause I made like 4 brooches lv 5 (3 sapphire) and I think should be around there.. but ofc it's not that reliable..