در خصوص ارتباط seo و سرعت سایت :
Site speed is only relevant when your site is extremely slow. Google doesn't penalize you unless your page load time is excessively long. You won't get a boost in rankings by speeding up your site.

With that in mind, Site load times do affect your user experience, so you may notice a lower bounce rate, more pages per visit, and possibly a higher conversion rate.
Google has indicated site speed (and as a result, page speed) is one of the signals used by its algorithm to rank pages. And research has shown that Google might be specifically measuring time to first byte as when it considers page speed. In addition, a slow page speed means that search engines can crawl fewer pages using their allocated crawl budget, and this could negatively affect your indexation.

Page speed is also important to user experience. Pages with a longer load time tend to have higher bounce rates and lower average time on page. Longer load times have also been shown to negatively affect conversions.
منابع + لینک های مفید :
https://moz.com/community/q/does-a-c...earch-rankings
https://moz.com/learn/seo/page-speed
http://googlewebmastercentral.blogsp...h-ranking.html
https://moz.com/blog/how-website-spe...search-ranking

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