The top gold and item find only applies to the chest. The legendary affixes apply to the whole map. This includes items not just from enemies but also the ones you get from Feats, Vendor and PVP chests. You want to save those maps for special occations like accomplishing they kill a Mythic monster feat. This will increase the quality of the eternal you get and give you a better average and higher chance of Crystal Eternal.
You can use Diamonds to reroll the map affixes to maximize the Luck affix if you wish. You can also use this to invrease your chances of an eternal Map via the same method.