One must be careful when discussing copyright protected materials in these forums. The vast majority of torrents are not legal, and mentioning that you are downloading a copyright protected movie will get the thread shut down.
This particular movie falls in a gray area of US copyright law (movies made prior to 1963), and if copyright was not renewed it could be in public domain. I seriously doubt that copyright wasn't renewed, so copyright should still hold until 2050.
Dutch law is the primary consideration at MyCE, but we voluntarily follow a stricter set of rules here in the forums than seen in Dutch home copy provisions. We try to follow a standard seen in most countries in regard to copyright provisions.
Therefore, we will not be discussing The Trouble with Harry unless you can prove that it is not under copyright protection at this time.
Your more general question about sizes of torrents is acceptable however. The size of torrents differ because the copies of the movies vary in the way they have been encoded.
This thread is now closed. If you wish to present evidence that The Trouble with Harry is not under copyright protection, please send me a personal message, and I will consider reopening the thread.