Optimizing a DAX Formula

I'm surprised this is slow, so I'm assuming you have many combinations of values based on the columns used in the matrix.  I would first look at the query behind the matrix using Performance Analyzer and try to reduce granularity.  If that can't be improved, I would use nested IF functions instead of SWITCH(TRUE().  Your expression forces all 3 variables to be evaluated every time.  Try to nest them so that you eliminate the most early on.

NewExpression =
IF (
    SELECTEDVALUE ( Contas[Grupo Conta] ) <> 62,
    "N/A",
    IF (
        SUM ( Principal[Real] ) > 0,
        "N/A",
        IF (
            SUM ( Principal[PO] ) > 0,
            "N/A",
            GE
        )
    )
)

Pat