767-300F is a perfect replacement for the MD-10-10's and I can see an eventual 767-400 based freighter replacing the few -30's we have. Unless there is a pretty significant shift in system form, however, no 767 variant is close to replacing the MD-11 the way we fly it now. Of course, as 777's continue to displace MD-11's off some of the traditional routes, we won't really need the extra lift of the Mad Dog so maybe the 767 is a "right-sizing." I'm voting for the Sonic Cruiser.