Never Opt for 2A in this train. Only book tickets in 2A if it's available or WL under 10. Anything above GNWL 10 in 2A of this train is risky affair. Saying from my own experience.
But SL and 3A have good occupancy and waiting clearance chances.
For 3A, till GNWL 20-25 is a safe side and in SL you can go till GNWL 50-60. You can get RAC.