What pages are you having trouble with? Most pages do not have images. The CPS library is the only one with images on every page. I have not noticed any speed issues, but my setup could be different from yours in many ways. I just need a little help finding the pages that are troubling you.
Any page. For example, the thread page that your comment, quoted above, was on. If I allow background images, scrolling becomes jerky, and moderately slow. If I use NoSquint to disable them, scrolling vertically is smooth, and very fast. It's the difference of a 2-3 seconds on scrolling a screens length, but multiple that by doing this repeatedly, for every time I scroll through a page of threads, or within a thread's pages, and it becomes a real nuisance. My CPU is fast, and I've got a good card. Can't say I've encountered this anywhere else, or before the site was renovated. For example, if I go to /forums.civfanatics.com/, or //forum.paradoxplaza.com/, it's not a problem. I can keep background images active, and scroll quickly without difficulty.
The main visual difference to the background that I notice, here, is that with background images enabled, the site screen seems to be on top of a mottled tan background, visible on both sides of the screen. It doesn't move when the site screen does, and it doesn't go away with resizing. Once background images are disabled, the mottled tan vanishes, and the active screen reaches to both edges.
If you need specific parameters of anything, I'll be glad to offer, but I'm not sure what you'd want at this point.