Rewrite SUMX? Poor performance when running calculations

I mean use IF statements which check conditions that could cause an error before main calculation. For example:

WeightedScore1 :=
ROUND (
        IF (
            CALCULATE ( SUM ( FactScore[Score1] ) ) > 0;
            CALCULATE ( SUM ( FactScore[Score1] ) ) / CALCULATE ( COUNT ( FactScore[Score1] ) );
            SUMX ( FactScore; FactScore[Score1] * FactScore[Weight1] )
            / SUM ( FactScore[Weight1] )
        );
    1
)

Another point is if you have many nested IF statements then it would be better use SWITCH function (following code is just an example):

SWITCH ( TRUE();
       CALCULATE ( SUM ( FactScore[Score1] ) ) > 0;
          CALCULATE ( SUM ( FactScore[Score1] ) ) / CALCULATE ( COUNT ( FactScore[Score1] ) );
       CALCULATE ( SUM ( FactScore[Score1] ) ) = 0; 
          0;
       CALCULATE ( SUM ( FactScore[Score1] ) ) < 0;
          SUMX ( FactScore; FactScore[Score1] * FactScore[Weight1] ) / SUM ( FactScore[Weight1] )
)