i play a very similar build and im actually taking it to a ptq and some big events and my sideboard has calcite snappers, frost titan and maybe jwar isle guy (blue rare besieged) since after game 1 your opponent will put in lots of removal to break combo and a 2nd win condition is brutal for them especially when they all have shroud.
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http://www.mtgvault.com/ViewDeck.aspx?DeckID=134453 .........heres mine
i would practice and mess around with your sideboard im not too big on it, but i like your main board. only advice---remove the prodigal pyromancer/sparkmage to sideboard and throw in goblin guides to mainboard. (and i definatly agree with more koths)