Let's say you want to send the same GPG/OpenPGP encrypted message to 50+ recipients. Assuming everyone you send to is trusted, and there is no risk of any recipient leaking their secret key, is sending a single message to multiple recipients less secure from an "ability to break" perspective?
Since GPG uses hybrid encryption, the message gets encrypted symmetrically with a key (the session key) that is encrypted asymmetrically.
Is the session key easier to figure out if you have 50+ asymmetrically encrypted strings that you know will all result in the exact same string when decrypted? (Though I realize that solving that session key would only compromise that specific message, and not any past or future messages from the sender or to any of the recipients.)
Would it then be more secure sending that specific message in batches of 5 or 10 recipients at a time? (or if you are paranoid, one recipient at a time) Even if the messages are identical, I would assume the session key is also generated with a timestamp or at least some form of non-deterministic factor in addition to the message hash. As a result each individual "5 recipient" message would end up with a different session key, and you would only have 5 encrypted versions of that key available.