The results of my tests by transferring a PRG file over the USB connection of KFF are as follows:
s[end] command (ef3usb.exe to KFF menu): 4s
e[xecute] command (ef3usb.exe to ef3usb.prg): 2s
I guess that the transfer code is better optimized in the USB Utilities (e command) than the EF3 one (s command). Unfortunately, it seems that the source code for the ef3executec.prg referenced in ef3usb.tas is missing in the EasyFlash 3 USB Utilities release. Maybe Tom-Cat can shed some light on this?
You can get it here: http://pc.sux.org/tomcat/ef3executec.prg