If you have f Feodums and s lots of 3 Silvers, then your total points (from Feodums) is p = fs. If we keep f + s constant (as does trashing a Feodum with >= 3 Silvers left), then the maximum value of p is when f = s (or s +- 1 if f + s is odd). Otherwise, we want to increase the lower value. So if s < f - 1, then trashing a Feodum will increase p, and if s = f - 1, p will remain constant.
tl;dr If you have less than 3 Silvers per Feodum then trashing a Feodum will result in your score staying the same or increasing.