This question hunted the mind of professional SEOs for some time now.
There is an approach to this issue:
Slow web page load time increases radically the changes that an user will exit your page before even seeing your content. This will create a big Bounce rate that will tell Google : this page is Worthless!!.
Keep as an advice and try to optimize your web page load for better user experience. The user is happy, Google is happy.
If Google is Happy… You are happy:)
We had integrated in our tool the web page speed checker from Google so you can easily click a button and check it.
We are an open to new ideas, if you believe that other external tools to be implemented in Darcy SEO Checker let us know, drop us a line and we will get back to you as soon as possible.
Check out this video from Matt Cutts:
Darcy SEO Checker Team