To be honest I have always run my shammies as 4 x elemental, healing the tank occ. with 4 x LHW when required so have never used my resto healing whilst boxing.

Saying that I use my resto to heal in raids and my main spam heal is chain heal. When starting the ICC heroics I also set up a heal spam on my tank which took advantage of the buff you get from riptide and chain heal which was:

riptide, LHW, LHW, chain heal, LHW, LHW repeat. I had my earth shield going up every 15-20secs.

Depending on the fight and your tank, this will single heal your tank through anything, whilst the chain heals should keep ur dps up through a lot of aoe, not to mention the crits from the LHWs restore mana and will heal the lowest health member of your group. My resto has slightly more mp5 than yours and about 40% crit when buffed and can spam this for more than 2 minutes quite happily which is generally more than enough time for any heroic boss.

Cheers