http1_read_buf_exact_size, http1_max_buf_size, and http1_title_case_headers are all configuration methods on hyper::client::Builder, but not hyper::client::conn::Builder. I notice that the methods are present on the latter type but are pub(super) rather than pub.
Currently, I believe users of the conn interface are stuck with the default values of these settings. Are there any reasons not to make these pub with similar docstrings to the higher-level API? I'd be happy to provide a PR if not.