Was Nagle enabled in 6.35 for server connections?
I'm not sure all servers have nagel's algorithm enabled. But I noticed it myself only a few+ years ago but not before then. If I use a ZNC on a host that doesn't do nagle, it actually gets packets to the server faster than connecting directly with mIRC.
I'm not really convinced that nagle is appropriate for IRC packets, being a slow form transport. Usually fewer than 1 outbound packet per second (way way way fewer). I don't think nagle provides any benefit for chat text streams, only large data streams with 3+ packets per second on average.