ARRL FMT -- getting the most accurate frequency

Everything you said it true, however the get_error command is only useful if the radio is GPS locked or locked to a 10MHz reference. The result does not take into account any drift in the internal OCXO or TCXO.
http://wiki.flexradio.com/index.php?title=TCP/IP_slice#GET_ERROR

Chuck, I'll have to defer to the folk at Flex as all I did was pull together the "How To" and don't have enough insight into the internal workings of the Flex. 

As to your results, the last 2 frequencies look to be the WWV frequencies less 1500Hz. Were you measuring WWV and providing the slice frequency?

As to the other 2, I don't recognize those. DId you used a signal generator referenced to a GPSDO to generate the 2 test frequencies then measured the error on the 6600 using the method outlined by Steve and documented in my PDF? If so, one possible factor could be that GPSDOs are extremely accurate when averaged over the long term but not as accurate for short term measurements. 

Ron

Practicing for tomorrow night received a Slice Get_error -45.774696 on my 6700 running 3.1.8

Ron, no problems with your document.

Always forget UTC starts the days B4 here thanks Dave