Sometimes I wonder what it would be if I had 4 Stifle instead of the Petals!!! Petals are good for 2 reasons. Generally, help in turn 1 combo (Sol-Land + Petal > Show and Tell + Fattie), and when a Grislebrand is out, so you can draw 7 or 14 cards to find a Petal and the other fattie. The first situation is very rare to happen, however the second one is very risky. Depends to your life total, if you're below 14 you just cant draw more than 7. I almost never sacrifice my Petal, to play Ponder or Brainstorm.
From the other side, Stifle is an answer to fetchlands, Planeswalkers, "comes into play - bounce" creatures like
Sower of Temptation or
Stingscourger, or
Karakas but the most important is to counter the Sneak's Attack delayed triggered ability.
I dont know... I have a good feeling about this. Ill test it out and come back for the results.