>From if_sl.c

 * SLMTU is a hard limit on output packet size.  To insure good
 * interactive response, SLMTU wants to be the smallest size that
 * amortizes the header cost.  (Remember that even with
 * type-of-service queuing, we have to wait for any in-progress
 * packet to finish.  I.e., we wait, on the average, 1/2 * mtu /
 * cps, where cps is the line speed in characters per second.
 * E.g., 533ms wait for a 1024 byte MTU on a 9600 baud line.

This last line is quite in error.  Waiting for 1/2 of a 1024 byte
packet is 512 / cps.  On a 9600 line, cps is 1200.  So that makes
a 426ms wait for a 1024 MTU at 1200 cps (9600).

 * EG: 426ms for 1024 MTU at 1200 cps (9600)
 * EG: 123ms for 296  MTU at 1200 cps (9600)
 * EG: 170ms for 1024 MTU at 3000 cps (~26400)
 * EG:  49ms for 296  MTU at 3000 cps <-------- typical v.fc
 * EG: 142ms for 1024 MTU at 3600 cps (~28800)

-john