DAX calculated column hanging - optimize or build in Power Query?

[macfuller]

I have a calculated column to categorize spend types in a 8+ million row table. The existing version posted below works, but I need to add one more variable (potentially doubling the number of categories) and when I try it works in the data model window but Excel goes bye-bye when I go into full calculation mode. No error messages, just sits after 20 minutes with 0% in task manager and "Ready Calculate" in the status bar. I guess it's the Excel equivalent of too much tequila - there's a pulse but no motion.

I'm hoping there's a way to optimize my DAX below so that I can squeeze in more categories. Otherwise I can build this in Power Query, but merging two 8+ million row tables and not being able to use VAR in M is a daunting prospect. Any recommendations are welcome!

=VAR POCreateDate =
    RELATED ( Orders[PO Date] )
VAR Scripted =
    RELATED ( Orders[IsScripted] )
VAR IsBkt =
    IF (
        RELATED ( Orders[Type] ) = "Blanket"
            || RELATED ( Orders[Type] ) = "Blanket Goods"
            || RELATED ( Orders[Type] ) = "Blanket Svcs"
            || RELATED ( Orders[Type] ) = "Svc Contract",
        TRUE,
        FALSE
    )
VAR IsElectronicPO =
    IF (
        RELATED ( Orders[PO Origin Description] ) = "Cart PO"
            || RELATED ( Orders[PO Origin Description] ) = "P/S Clinical Service Inventory",
        TRUE,
        FALSE
    )
VAR AfterFactRule =
    IF (
        IsElectronicPO,
        Vouchers[Invoice Date] >= POCreateDate,
        Vouchers[Invoice Date] >= POCreateDate + 1
    )
RETURN
    IF (
        LEFT (
            Vouchers[PwC Category],
            2
        ) = "A)",
        "Excluded Spend",
        IF (
            Vouchers[PO Number] = "",
            "Non-PO",
            IF (
                ISBLANK ( POCreateDate ),
                "Unclassified PO - No History",
                IF (
                    IsBkt,
                    IF (
                        AfterFactRule,
                        IF (
                            Scripted = "Catalog",
                            "Controlled Blanket PO",
                            "Scripted Blanket PO"
                        ),
                        IF (
                            Scripted = "Catalog",
                            "After-the-Fact Blanket Catalog PO",
                            "After-the-Fact Blanket Scripted PO"
                        )
                    ),
                    IF (
                        AfterFactRule,
                        IF (
                            Scripted = "Catalog",
                            "Controlled Regular PO",
                            "Scripted Regular PO"
                        ),
                        IF (
                            Scripted = "Catalog",
                            "After-the-Fact Regular Catalog PO",
                            "After-the-Fact Regular Scripted PO"
                        )
                    )
                )
            )
        )
    )