Against combo I really like Pirostatic Pillar. It buys us several turns and deals some damge while the opponent plays some brainstorm/cunning wish/burning wish and the removal/bouncer. This damages (easily 4-6) combined with the damage we can deal during those turns we have won (and consider that we have some more since the opponent would have trashed some tutors/draw) my finish the opponent. Of course its a hard matchup, but I don't think we can stop them, we just need to buy 4-5 turns. If a deck is faster than us, then, we should change things to slow them down.
You have no way to slow them down... the only combo deck that you would hope to beat with this deck is Emdlin's SI, and you would have to survive until turn 2 to do so.... Out of all seriousness, if I were playing this deck and was paired against combo, I would scoop to save both of us some time... although there isn't much saved time there...

The thresh MU doesn't look all that bad, seeing as everything is a threat, but I have beaten burn with thresh in the past, so it cannot be all that bad for them, seeing as they now have ways to prevent the damage (i.e. destroy your creatures/ block them to hell).