SASI indexes on year and month - cassandra

Question

I am new to SASI indexes in Cassandra and I am unclear how they index when multiple columns are included in the "where" predicate that are indexed.
Here is one option I am looking at:
Option 1:
CREATE TABLE IF NOT EXISTS my_timeseries_data (
id text,
event_time timestamp,
value text,
year int,
month int,
PRIMARY KEY (id, event_time)
) WITH CLUSTERING ORDER BY (event_time DESC);
CREATE CUSTOM INDEX year_idx ON my_timeseries_data (year)
USING 'org.apache.cassandra.index.sasi.SASIIndex'
WITH OPTIONS = { 'mode': 'SPARSE' };
CREATE CUSTOM INDEX month_idx ON my_timeseries_data (month)
USING 'org.apache.cassandra.index.sasi.SASIIndex'
WITH OPTIONS = { 'mode': 'SPARSE' };
I expect to query like this sometimes:
select * from my_timeseries_data
where year = 2016 and month = 1 ALLOW FILTERING;
Does the SASI index on 'month' column help my performance?
Option 2:
Would it be better to index a concatenated column like 'year_and_month' below?
CREATE TABLE IF NOT EXISTS my_timeseries_data (
id text,
event_time timestamp,
value text,
year_and_month text,
PRIMARY KEY (id, event_time)
) WITH CLUSTERING ORDER BY (event_time DESC);
CREATE CUSTOM INDEX year_idx ON my_timeseries_data (year_and_month)
USING 'org.apache.cassandra.index.sasi.SASIIndex';
And then query like this on a single SASI index:
select * from my_timeseries_data
where year_and_month = '2016_1';
Option 3:
NO need for extra month and year columns and SASI indexes because having 'event_time' as a CLUSTERING COLUMN allows scalable time-range queries that I want to do anway?