email packet length size

Message length quantization is necessary for security in a remailer network. Right now there's not enough traffic through the remailers to warrant more than one such quantized length. What length should that be? This information can be readily calculated from the length distribution of the current messages passing through the remailers. If only one or two remailers would instrument their devices in order to record just lengths, that would provide the necessary data. Any volunteers? My complete guess is that it's going to be around 4-5 KB. Eric