I have a very simple website, but somehow dated, that works flawlessly here : [lyaudet.eu/laurent](https:/lyaudet.eu/laurent/). There is no server side rendering, only static XHTML pages and a CSS file. I already know that static files are very performant and have a low carbon footprint, so please no answer like "It does not matter, just take the latest technology.". I want to know how much difference there is in the latency and navigator energy consumption between HTML5 files and XHTML files, since the syntax of XML is simpler than the syntax of SGML. I assume that both static HTML5 and XHTML files are valid without error or warning here: validator.w3.org. Answers like :

• "For 10KiB webfiles, XHTML latency is between x1 and y1 and carbon footprint is between z1 and t1, whilst HTML5 latency is between x2 and y2 and carbon footprint is between z2 and t2",
• or even like "For 15KiB webfiles, XHTML latency follows approximately a normal distribution like..."

I tried to look at speed tests and online carbon footprint calculators. But I was wondering if public or corporate researchers studied this question (or a broader one) with some kind of "reference webpages". I checked also on the Internet including this question link