That site is very useful but as you noticed you need to adapt the information to your own situation. I used that site a great deal when redesigning my own site . I have seen many sites that download VERY slowly and based on what I learned would look at images. The biggest culprit to slow download speed is not the numbers images but the size of images. People will often include jpeg images for their sites that are 150kB when all they need is 15kB. I use the “save for web” feature on Adobe Photoshop Elements to optimize my image sizes for the web. One recent analysis of my site showed that the Authorize.net logo/authentication at the bottom added quite a bit of time. That one surprised me.