Hi, I am in a unique position to answer this question with facts. I assume you are talking about the time taken for a page to “appear” on your fast internet connected new MacBook.
My RapidTemplates run on both the Foundation blank theme and also S4S’s ThemeFlood Bootstrap based Blank Theme. Therefore, by just selecting the theme Foundation or Blank Theme I can compare both back to back. In the tests that I and customers have done, there is no detectable difference in page loading using the same project file. That is a fact based on real world observations. They are both excellent, fast, well supported, continually developed and mature. Also, as I am completely impartial and have no commercial relationship with framework builders, stack vendors or “other”, so I will just report it just how it is with no smoke and mirrors. Now, we can spend hours debating which is better, more shiny and smells better but there is no detectable difference in performance. A growing trend on this forum has been for members to promote one and bash the other.
If you are talking about sites using Joe workman Foundation stacks suite (of which I have a great deal of experience), then I don’t think you will find a faster performing, mature, well documented, continually developed, dedicated multi-forum supported, dedicated 3rd party Plus support and optimised complete suite of stacks.
If you are talking about my Projects and Templates then some are loaded up to “infinity and beyond” with animations and effects to show many of the amazing things possible. This obviously slows things down but certainly not to an unacceptable level. These are not designed to be used in a real world site with all animations and effects working together as that would be silly. My Template 3 “The Grid” for example has Ken burns slow zoom and pan, with additional CSS blur, brightness as well as scaling web fonts with animated path transitions in a multi grid responsive layout. Yet the whole grid will scale elegantly before your eyes and if you had a cent for every calculation going on in the background, you could run with Donald Trump.
All web animations need to be treated with careful choice in a final design but in a demonstration more animations than is optimal may be used just to illustrate what is possible.