yes, the serial port cables are slower (in data tranfer) than the usb cables, we tried with much of lg with samsung, the lg series which usually convert the serial port in to usb ports, the speed is considerably slower than usb, (to check for speed may use speedometer at macfee.com)
lg speed is 32-40 Kbbs
samsung ahead to 82 Kbbs
yes it is real,
if you particular when down loading use always samsung series in cdma, (samsung is withdrawn or not availble, But samsung 191 is net worth for net use)
with regards