Now that we are 24h before end of season, we can see the CP/Dec spread has been cut in half from the time I posted this

At these rates, getting the 3 additional loot chests for being in silver II compared to silver III is going to cost 35000(cp needed) / 37 (CP Dec Spread) = 945.9 DEC spent on CP for those 3 additional loot chests.

If you are taking the gamble, I wish you luck.