Reducing CREATE TABLE overhead?

I have a simple SQL query: SELECT * FROM table; - a simple sequential scan - which takes me 10s. When I add CREATE TABLE AS (CTAS syntax) to it, i.e. my query is CREATE TABLE db_test AS SELECT * FROM table;, the query now takes 18s. I could not see any notable difference between the plan. What are the steps I can take to minimize this 8s overhead? I have already tried using UNLOGGED keyword.