[atlas] probe resolution, overhead, or ...?

we want to use atlas probes in an experiment.  being prudent (you can
tell it was not i), we decided to try to get some basic calibration.
one run was just on a local LAN.

three hosts on the same gige switch
  o probe 2285
  o psg.com, a not very fancy or fast freebsd 9 box with intel/pro1000
    gige ports
  o bbgp.psg.com, a funky older freebsd 9 box with bge gige

probe 2285 pinging bbgp.psg.com, average RTT: 1.5606994382 [0], number
of pings: 356*3

psg.com pinging bbgp.psg.com, average RTT: 0.253424332344 [0], number of
pings: 674

has anyone done similar probe calibration experiments?  does anyone have
any clue as to why the difference?

randy


[0] - my favorite precision joke
    A gentleman accosts a guard in the museum and asks, "How old is that
        mummy?" 
    The guard responds, "I believe it is 2005 years old."
    The gentleman asks "Why that particular age, 2005?"
    The guard responds "Well, I was told it was 2000 years old when I
        started work here five years ago."