Your message was unreadable, you should use text form for messages sent to the ITS.
In any case, according to many sources, the default values for TCP buffers can be pretty small. Usually, they can be configured system-wide at the OS level (see tcp(7)), or even auto-tuned.
Personally, I have no objections in optionally allowing to hard-set the buffer sizes to values one considers appropriate for the intended use of slapd. Since the optimal size roughly depends on latency and bandwidth, this may probably need to be configured on a per-listener basis, actually.
However, in deployments where this problem becomes critical, usually hardware dedicated to slapd is used, so system-wide tuning (and auto-tuning) would be the preferred option anyway. Manual setting should be used only when system-wide or auto-tuning is not available or accessible for some reason.
p.