I'm experimenting on two accounts, I'm upgrading one to silver 3 and other will remain in bronze.
I'll keep record of rewards and DEC gain for the two accounts and post the results.
But for the first day, I can say it is a lot cheaper to farm DEC at bronze 1 (important to have the power), opponents are easier and you get 5-11 DEC per win.

A special mention to @spl_godislove777 that allowed me to try this by delegating me a card worth 20k power. <3