I do not have an item list for you nor do I have any math or spreadsheets worked out, but I have played a shaman for a very long time. Normal bonus healing and spell damage works the same for pvp. Spell power is definitely awesome in pvp for ele, as is crit, as the limited encounter uptime vastly decreases your dependence on having a huge amount of int (which I find preferable for ele pve gear). I would advise you to get general bonus spell damage & healing gear as your shocks frankly do quite a lot of damage and your survivability will be bolstered hugely by the +heal, but nature damage is definitely great if you have access to really strong nature damage gear.
