Ok assuming all your values are numeric then try this:

in the where clause

CHARINDEX('.',col1) > 6

OR

(CHARINDEX('.',col1) = 0 AND LEN(col1) > 5)

Here is my example for returning values that would overflow.

DECLARE @Tmp TABLE

(COl1 VARCHAR(100))

INSERT INTO @Tmp

SELECT '1' UNION ALL

SELECT '1' UNION ALL

SELECT '1' UNION ALL

SELECT '1' UNION ALL

SELECT '1' UNION ALL

SELECT '1' UNION ALL

SELECT '1' UNION ALL

SELECT '1' UNION ALL

SELECT '1' UNION ALL

SELECT '92345.1234567' UNION ALL

SELECT '12345.12345671' UNION ALL

SELECT '123456.1234567' UNION ALL

SELECT '111111111111111111111111111111' UNION ALL

SELECT '1234567890'

SELECT

--CAST(col1 as decimal(12,7))

col1

FROM @Tmp

WHERE

CHARINDEX('.',col1) > 6

OR

(CHARINDEX('.',col1) = 0 AND LEN(col1) > 5)