I've had to up the maximum simultaneous connections, but otherwise I've been able to log extremely large volumes of data from 1,000s of machines, with syslog-ng. I'd assume the same is true with rsyslog.

Looking at limits on open files, and considering tcp timeouts and cookies were all we needed. Total volume was in the order of high 10s of GB.

If you want to unpack offline, contact details are in my profile.