Educated guess about RDS instance with best performance to cost ratio based on EXPLAIN ANALYZE of PostgreSQL

I have a table that stores 1M 384-dimensional vectors in the column called vector of type "char"[]. Consider the query:

EXPLAIN ANALYZE
WITH Vars(key) as (
    VALUES (array_fill(1, ARRAY[384])::vector)
)
SELECT content_id
FROM MyTable, Vars
ORDER BY vector::int[]::vector <#> key
LIMIT 10;

The key is just a toy vector consisting of all ones. <#> is the dot product operator of the pgvector extension, and vector is the type defined by that extension, which to my understanding is similar to real[].

Here is the output when running on db.m7g.large RDS PostgreSQL instance:

 Limit  (cost=83268.20..83269.37 rows=10 width=12) (actual time=3070.513..3070.570 rows=10 loops=1)
   ->  Gather Merge  (cost=83268.20..180496.59 rows=833328 width=12) (actual time=3070.512..3070.567 rows=10 loops=1)
         Workers Planned: 2
         Workers Launched: 2
         ->  Sort  (cost=82268.18..83309.84 rows=416664 width=12) (actual time=3062.863..3062.864 rows=8 loops=3)
               Sort Key: ((((mytable.vector)::integer[])::vector <#> '[1,1, ... ,1]'::vector))
               Sort Method: top-N heapsort  Memory: 25kB
               Worker 0:  Sort Method: top-N heapsort  Memory: 25kB
               Worker 1:  Sort Method: top-N heapsort  Memory: 25kB
               ->  Parallel Seq Scan on mytable  (cost=0.00..73264.22 rows=416664 width=12) (actual time=0.017..3005.128 rows=333333 loops=3)
 Planning Time: 0.097 ms
 Execution Time: 3070.597 ms
(12 rows)

Given this output, how can I make an educated guess about which of the many instance types will give the best performance to cost ratio for this particular query?