I use Genesis for all my 9 sites and site speed is what concern me the most, I choose plugins very carefully and even if on my popular site with more than 10k visitors/day I have 30 plugins installed, the page load is under 2 sec. (dedicated server, AdS and Analytics). I have tested Jetpack and I'm not exactly happy to run additional scripts on homepage and archive when I only use the comments module, this is a nonsense even if I really like its functionality.