DECLARE @TheDateTime DATETIME

SET @TheDateTime = '20160630 20:21:22'

SELECT CASE WHEN @TheDateTime = CAST(CAST (@TheDateTime AS NVARCHAR(50)) AS datetime) THEN 'All Correct' ELSE 'Fail!' END [Cast performance],

CASE WHEN @TheDateTime = CONVERT(DATETIME, CONVERT (NVARCHAR(50), @TheDateTime, 109), 109) THEN 'All Correct' ELSE 'Fail!' END [Convert performance]