Site performance can impact search rankings on Google and Bing, True Or False? and Why?

Scientific article which is the most important and the order of pages and continuous updating

Well whether we go for the clarification that it's true or false the most important thing is that if your site is well optimized with perfect keyword stuffing not too much with user-friendly content then it means that your site is performing well and it will attract more audience and will remain in top list of search engines.

Google:

Site speed has a weight-age in rankings. Perhaps not important as it used to be but, still...important. 

Bing:

In my personal experience, Bing does not give as much importance to this factor.

Please, not the site speed speed is important in any case. Do you want your target user to sit waiting for your page to load. if the site is bad it's bad.

Don't know about Bing, but as far as Google is concerned site performance is definitely a factor that is counted for ranking purpose.There is not clear explanation about why (atleast I haven't come across any). But the reason has to be obviously that the user has too many options to choose from. And the one that offers the right solution at shortest period of time will be preferred by user.