If I do understand you correctly you are asking whether you should issue the queries one after the other or concurrently, I have trouble to understand your pseudo code…
You need to benchmark this on realistic resultsets, under realistic load…
Doing the queries concurrently will result in more copying of the result sets as each query happens in another process
Doing the queries concurrently will result in more exhaustive use of your connection pool, so other requests/processes in your application might need to wait more time until they get a connection to the database
These are my two main issues I do see with querying concurrently.