I have a similar experience - after a redesign and significant improvement of page load time, the bounce rate and few other metrics improved but conversion rate

I have a similar experience - after a redesign and significant improvement of page load time, the bounce rate and few other metrics improved but conversion rate stayed almost exactly the same. Kissmetrics are probably measuring this across thousands of sites and averaging the results as opposed to taking a slow site and tracking conversion rate after it gets speedier. So, it could be a correlation kind of thing - better sites, with more resources, simply invest more into every aspect of the business, including site speed.