(1) If this is a recurring issue, you might want to consider tools like
cfengine and
puppet, which are designed to automate system administration tasks for large numbers of machines.
(2) If doing 50 concurrent file transfers causes unacceptable network congestion, you might consider using the bit torrent protocol to distribute the file internally from a local server (like Bloodnok's suggestion, but with a different protocol). Bit torrent is effectively cooperative so that the entire 50 GB does not have to come from a single source (host).
(3) Finally, let me pile on the anti-telnet bandwagon. It is simply a bad idea to run a telnet server in most circumstances. If ssh seems to have too great an overhead, you can greatly reduce its overhead by using a weaker cipher (eg, "ssh -c arcfour hostname"). This does not affect the protection given to the authentication mechanism.
