Customized Theme for Blog

Hello

If I am to develop a blog for someone or a client, should I create a theme with reduced php functions for better speed?

Or should I make it like a regular theme downloaded from anywhere?

ex) bloginfo() can be replaced with HTML and is not necessary. and there are whole bunch of unnecessary php codes.

I understand if the customer would have a multiple usage of the theme, but if he knows he is using this theme for 1 blog, I think I should make it customized.

Also, is get_header(), get_sidebar(), get_fotter() something that would make the website faster or slower? I know it reduces the size of file, but wouldn’t php make it slower than just hardcoding?

Thanks in advance