If England can get close to 250 ahead (and yes; it's a long way away right now), it could still be an interesting final innings. But you'd have to fancy the Sri Lankans from where we are right now. 175 - 200 wouldn't be enough to defend, in my opinion.
200 will make it interesting and don't forget there is a different pressure for Sri Lanka when they should be getting a score and winnings the game