I’d suggest testing just https - Netlify will always redirect for http, but repeat visitors will start out on https saving the redirect :).
Our staff can’t really “support” what performance testing tools say - you can ask their author for help with that. If you have some specific slow request that you’d like advice on, we can help with that - please make sure you include the x-nf-request-id value for such a request, as described here: [Support Guide] Netlify Support asked for the 'x-nf-request-id' header? What is it and how do I find it?