Is there any significant difference between Month(date) and DatePart(month, date)?
I just ran several tests on a largish table (12,430,129 rows) in SQL Server 2008r2.


The field is smalldatetime
The field is NOT indexed
I changed the processing order after each run to eliminate page caching issues


Results:

MONTH() - Ran in 6662, 6583, 6661 and 6560 ms.  Average runtime 6616.5ms

DATEPART() - Ran in 6520, 6584, 6552, and 6608 ms. Average runtime 6566ms

So, DATEPART() does seem to be marginally faster.  However, this is 7 tenths of a percent difference, so it probably won't matter a whole lot.