The difference between HTTP and https is one is secure, and the other isn’t.
In the earlier day of the web, I remember few web sites used https. Mostly when it comes to eCommerce sites, to secure credit card transactions. Today the web is much different and the tables have turned. Now you rarely see web sites without using https.
A Selection of Pages Related To HTTP vs HTTPS
Is Https Slower Than Http?
Naturally since https is secure and more checks are needed before a web page is displayed, https will be slower than a http connection. But now with most sites being secure and advances in technology I no longer sense a difference in speed.
Have a look at the web pages below I have selected that go into depth about this topic.
Web Pages I have Selected Related To The Speed of http vs https
HTTPS SEO Impact
https now is a ranking factor for Google. All things being equal, a site using https will outrank a site that uses HTTP.
That being said, does that mean if you switch from HTTP to https your page will move to the tips of the SERPs? Not at all. There are over 200 ranking signals and this is just one.
Have a look at the articles I have selected below for more on the impact of https regarding search rankings