I am looking at the same decision between Silver and Gold. Since I spend half of the season in Silver I am thinking that I will receive 10 more chest playing Silver than Gold. Thus the %chance of getting a gold or Legendary card is higher with the increase in number of chest.

I agree staying in Silver will give me a baseline for future decisions. I will also get to see if I easily get more than 4 chest per day in the focus quest.
!PIZZA