Efficient SUMX aggregation - best practice

With the help of members in this post I have a measure [BankOD RT] which calculates a running total overdue balance. I need to aggregate this across all open accounts (c 1,800 accounts open out of 15,000) and all transactions (c 3,000,000).

The  filters I would like are:

// Only Open Accounts
DimAccounts[status] = 1 or DimAccounts.[ClosingDate] > [maxDate]

// No Deposit Accounts
DimAccounts[ProductType] <> "D"

// Overdue balance for this account > $200
[BankOD RT] > $200

The result will be a page with:

• Slicer for selection of month context
• Table visual showing count open accounts and sumx of [BankOD RT]

Since it is only creating one aggregated output figure, does this use CALCULATETABLE? How can I filter the SUMX