I recommend a buffer size of at least 1MB, but 2MB provides even more protection against a data flow outage. When data is sent from the computer's hard drive to the recorder, it fills the recorder's buffer with data before it's received by the laser record head. A separate CPU in the recorder moves data in the buffer to the record head at the required demand rate. If an outage occurs at the input of the buffer, the recording session isn't affected as long as some data already exists in the buffer. A full 2MB buffer can deliver data to the record head with up to a three-second data outage from the data source at the X1 speed.
Faster speeds are less forgiving.
The larger buffers on the new machines yield yet another benefit. Let's say you're using one of the higher record speeds coupled to a system that can just barely keep up with the data demand. With the earlier machines it spelled disaster and you had the dreaded buffer underrun. Recorders today with the larger buffers can actually sense the loss of data at the buffer's input and, since the buffer is large enough, permit proper closure of the track. Even on large single sessions that will normally fill up a CD, I recommend you leave about 10MB free on the first session and close the disk as a separate final session.