Yes 40MB should be strongly considered. Can't be specific on this one. Depends on your content, your computer. Some people have almost no text, almost all images. Others are the reverse.
When you publish/preview that 40MB expands into separate pages, separate images and can actually take up far more room. Windows ties up resources to convert your files. The larger the file, the more likely you will face publishing issues, and corruptions and lose the ability to do a FILE SAVE AS and give the file a new name. That means you can no longer compact the file to trim out unused code! Compacting helps the file TREMENDOUSLY! Adds life and longevity to the file.
Successful publishing up to 180MB files have been reported. BUT WOW! If you moved that to a new host, or new computer, you would have to publish that WHOLE FILE from scratch again. Can't say what would happen for you but I can tell you that I would not be able to publish that whole file without locking up or disconnecting from the server several times!!!
I try to plan my web layout to keep my files under 25MB, preferably under 20MB.
I have several that are less than 10MB.
When I expect to add a bunch of new pages, I consider if they should be added to the existing files or begin a new section.
