Comment on WordPress SEO by SEO Dave.
Stallion uses Timthumb for some of the thumbnail images to keep sizes down (Timthumb creates small thumbnails), if you use the Stallion thumbnail option and make sure all posts have Stallion featured images or WordPress featured images all your posts and pages thumbnails will be relatively small in size. If you don’t set these a thumbnail could be a full size image from within a post/page which will slow loading on the home and archive pages. I’m lazy and haven’t set all mine yet :-)
If you’ve been using the Contextual Related Posts plugin from this site I’ve made another version at WordPress SEO Plugins (calling it Stallion Related Posts WordPress SEO Plugin) which uses Timthumb built into Stallion for the thumbnails, so this will reduce the load on the images as described above. When I update Talian I’ll add the option into the related posts plugin for Talian as well.
Other than that I use Corel PhaintShop Photo Pro and optimize the sizes best I can without degrading the quality too much, but if you want images on a site it slows things down. Price you have to pay for a nice site I’m afraid :-)