Duplicate Across Multiple Tables

I need help in planning the best course of action to find duplicates from multiple tables.

     

    DECLARE @Table1 TABLE (ID_T1 int, Col1 varchar(10), C2 varchar(10), C3 varchar(10), C4 varchar(10), Col5 varchar(10), Col6 varchar(10))
    DECLARE @Table2 TABLE (ID_T2 int, Col1 varchar(10), C2 varchar(10), C3 varchar(10), C4 varchar(10), Col5 varchar(10), Col6 varchar(10))
    
    INSERT INTO @Table1 (ID_T1, Col1, C2, C3, C4, Col5, Col6)
    SELECT 1, 'One', 'Test1', 'Line1', 'Record1', 'OTLR1', 'RLTO1'
    UNION ALL
    SELECT 2, 'Two', 'Test2', 'Line2', 'Record2', 'OTLR2', 'RLTO2'
    UNION ALL
    SELECT 3, 'Three', 'Test3', 'Line3', 'Record3', 'OTLR3', 'RLTO3'
    UNION ALL
    SELECT 4, 'Four', 'Test4', 'Line4', 'Record4', 'OTLR4', 'RLTO4'
    UNION ALL
    SELECT 5, 'Five', 'Test5', 'Line5', 'Record5', 'OTLR5', 'RLTO5'
    UNION ALL
    SELECT 6, 'Six', 'Test6', 'Line6', 'Record6', 'OTLR6', 'RLTO6'
    UNION ALL
    SELECT 7, 'Seven', 'Test6', 'Line6', 'Record6', 'OTLR7', 'RLTO7'
    UNION ALL
    SELECT 8, 'Eight', 'Test8', 'Line8', 'Record8', 'OTLR8', 'RLTO8'
    INSERT INTO @Table2 (ID_T2, Col1, C2, C3, C4, Col5, Col6)
    SELECT 10, 'Ten', 'Test1', 'Line1', 'Record1', 'OTLR10', 'RLTO10'
    UNION ALL
    SELECT 20, 'Twenty', 'Test2', 'Line2', 'Record2', 'OTLR20', 'RLTO20'
    UNION ALL
    SELECT 30, 'Thirty', 'Test3', 'Line3', 'Record3', 'OTLR30', 'RLTO30'
    UNION ALL
    SELECT 40, 'Forty', 'Test4', 'Line4', 'Record4', 'OTLR40', 'RLTO40'
    UNION ALL
    SELECT 50, 'Fifty', 'Test5', 'Line5', 'Record5', 'OTLR50', 'RLTO50'
    UNION ALL
    SELECT 80, 'Eighty', 'Test80', 'Line80', 'Record80', 'OTLR80', 'RLTO80'
    UNION ALL
    SELECT 90, 'Ninety', 'Test90', 'Line90', 'Record90', 'OTLR90', 'RLTO90'
    SELECT * FROM @Table1
    SELECT * FROM @Table2

Now, C2, C3, and C4 can have either unique or duplicate values in Table1 and Table2. 

I am trying to get three outputs.
Output 1 will have ONLY the records from Table 1 which has same C2, C3, and C4 columns' values in table 2 with Duplicate marked as 1/0 in Duplicate_SameTable

Output 2 will have ONLY the records from Table 1 which has same C2, C3, and C4 columns' values in table 2 with Duplicate marked as 1/0 in Duplicate_PrimaryTable

Output 3 will have the records from Table 1 and Tabl2 2 which has same C2, C3, and C4 columns' values with Duplicate marked as 1/0 in Duplicate_BothTables.

I can get the Output 1 from the following query.

    SELECT *, CASE
    			WHEN COUNT(*) OVER (PARTITION BY  C2, C3, C4) > 1 THEN 1
    			ELSE 0
    		 END AS Duplicate_SameTable
    FROM @Table1
    ORDER BY ID_T1 ASC

Output 2 

    SELECT B.ID, B.Col1, B.C2, B.C3, B.C4, B.Col5, B.Col6, CASE WHEN C.Duplicate_SameTable = 1 THEN 0 ELSE B.Duplicate_BothTables END AS Duplicate_PrimaryTable
    FROM (
    SELECT ID, Col1, C2, C3, C4, Col5, Col6, CASE
                WHEN COUNT(*) OVER (PARTITION BY  C2, C3, C4) > 1 THEN 1
                ELSE 0
             END AS Duplicate_BothTables FROM ( 
    SELECT ID_T1 AS ID, Col1, C2, C3, C4, Col5, Col6 FROM @Table1
    UNION
    SELECT ID_T2 AS ID, Col1, C2, C3, C4, Col5, Col6 FROM @Table2) A
    ) B INNER JOIN (SELECT *, CASE
                WHEN COUNT(*) OVER (PARTITION BY  C2, C3, C4) > 1 THEN 1
                ELSE 0
             END AS Duplicate_SameTable
    FROM @Table1) C ON B.ID = C.ID_T1

Output 3

    SELECT B.ID, B.Col1, B.C2, B.C3, B.C4, B.Col5, B.Col6, CASE WHEN C.Duplicate_SameTable = 1 THEN 0 ELSE B.Duplicate_BothTables END AS Duplicate_PrimaryTable
    FROM (
    SELECT ID, Col1, C2, C3, C4, Col5, Col6, CASE
                WHEN COUNT(*) OVER (PARTITION BY  C2, C3, C4) > 1 THEN 1
                ELSE 0
             END AS Duplicate_BothTables FROM ( 
    SELECT ID_T1 AS ID, Col1, C2, C3, C4, Col5, Col6 FROM @Table1
    UNION
    SELECT ID_T2 AS ID, Col1, C2, C3, C4, Col5, Col6 FROM @Table2) A
    ) B LEFT JOIN (SELECT *, CASE
                WHEN COUNT(*) OVER (PARTITION BY  C2, C3, C4) > 1 THEN 1
                ELSE 0
             END AS Duplicate_SameTable
    FROM @Table1) C ON B.ID = C.ID_T1
    ORDER BY B.ID

I am wondering how to go about getting Output 2 and Output 3  more efficiently. 

One way I can think of doing is Union Table 1 and Table 2 and then run above query. Or is there a better way of doing this as real tables will have millions of records and doing UNION and then applying above query might take much longer.

Thank you