I have a banner and some social media buttons added through a template edit. I was wondering if it would be better to put it in a block or leave it as is. My goal is better performance.
Technically putting things straight into a template may have better performance.
However if you create a static block and make sure it is cachable on the whole site the difference will be negligible. There are many other ways to improve performance and this is right a the bottom of the pile.
There are many other things that you can do to improve performance. Taking the view of the site as a whole. The flexibility that a block gives you may give you may outweigh the performance gains you achieve.