Permalink Settings

I don’t really want to display date in the URL of a blog, but I have read that a first option in permalink needs to be a number for speed reasons. It said that sites that just display blog name and they have a lot of blogs, they will suffer from slow loading site.
Since I don’t want to display the date, I have created this Custom Structure:
/%post_id%/%postname%/

Will this help my site from suffering from slow loading speeds, and will there be any SEO issues from not displaying the blog date in the URL?

And also, will there be any issues if one site on my multisite installation is using above mentioned code and another site uses standard:
/%year%/%monthnum%/%postname%/
And maybe 3rd site is using some other permalink configuration.