Performance penalty when requesting text values in binary format

I'm the creator of the PostgreSQL driver pgx (https://github.com/jackc/pgx) for the Go language. I have found significant performance advantages to using the extended protocol and binary format values -- in particular for types such as timestamptz.

However, I was recently very surprised to find that it is significantly slower to select a text type value in the binary format. For an example case of selecting 1,000 rows each with 5 text columns of 16 bytes each the application time from sending the query to having received the entire response is approximately 16% slower. Here is a link to the test benchmark: https://github.com/jackc/pg_text_binary_bench

Given that the text and binary formats for the text type are identical I would not have expected any performance differences.