If we lead by over 400 runs then it will be impossible for SA to win. The question is when do we declare. How much time our bowlers need to take 10 wickets? Also whether there is any possibility of rain. I think we should bat till one hour after lunch and then declare. In 3 hours of batting before that we should be able to add at least 150 to 175 runs. So total lead will be around 475+. With this lead we won't lose the match. Whether we will win depends on Zak, Ishant and Shami. On 4th and 5th day pitch even Ashwin should trouble the batters. By close of play tomorrow, picture will be clear. Fingers crossed!