reply to u/ingeniouskeys at https://www.reddit.com/r/typewriters/comments/1e0utt9/differences_between_olympia_sge_typewriters/

The Typewriter Database is going to be one of your better sources, but will require delving into each particular exemplar to see what their owners may have written about them. So, for example, go to https://typewriterdatabase.com/Olympia.SGE40.61.bmys and then click on the individual galleries for all the machines. If you've got an account, you can message those who currently have them and ask questions directly.

Given their manufacture in the late 60s and into the early 70s you're likely to find small incremental improvements in the electrical side, but you're also likely to find more dramatic changes in manufacturing which made them cheaper (replacing metal pieces for flimsier plastic.) I doubt the 45 (later 70s) is going to be incredibly much better than the 40, which I would suspect to be more robust from a manufacturing standpoint. You may have vaguely better "specs", but its build quality is likely going to suffer even more, so you'll have to balance out what you're after.

If you want to delve into the deeper specifics, then try out the repair manuals for them: https://www.lulu.com/shop/ted-munk/the-olympia-sge-304050-typewriter-repair-manual/paperback/product-1e4pnd4v.html?page=1&pageSize=4