As I stated in my comments, IF the queries are (almost) always for birthdays in a month / range of days, a clustered index on a base-dated dob should give...

There actually is, in theory, a fundamental difference between those queries:

The first query will drop/ignore any row that does not have a matching row in the Account table,...

I suggest you do it this way, which will make the output easier to use (at least for me):

DECLARE @command varchar(1000)
SELECT @command = '

It makes zero sense to pull out just the month and index it.  You'd be far better off indexing the date with a dummy year.

And if one (almost)...

I have used views for that, but only for a very limited number of values, since it can't be effectively indexed.

Unique indexes are potentially extremely valuable, even for...

Or take a step back and consider whether "dob" shouldn't be stored as separate columns to begin with, in accordance with standard data normalization (if you need to constantly look...

While it's still available in the cache, just at it would be for index_usage_stats, you can likely use:
sys.dm_db_index_operational_stats

If the table is active, that data is very...

As a very slight simplification, you could also do this (I prefer CAST when possible since it's ANSI-standard, whereas CONVERT is not):

CAST((CP + 9) / 10 AS int)

The key thing to remember is this:
Data does not have to stored in physical sequence in order to be able to read in key sequence.

That is, the...