Dave, how accurate are the Rigol 10Mhz out compared to your Rubidium standard. ?
Without even testing it, I can tell you it's crap. Same as the internal crystal in the Agilent counter.
There's another issue with the Rigol time base that surfaces in the function generator. I have a DG-4102 and found that there's a lot of phase noise and/or jitter on the output when using the internal time base. But the output cleans up very nicely when the DG-4102 is clocked with a high quality external time base.
The two plots below show the difference. Test setup is to put the DG-4102 to Sine output at 10.050 MHz, and connect that to a frequency mixer (in this case, I used a Mini-Circuits mixer) and the second mixer input to a known high quality clean crystal oscillator (in this case, an HP oven 10 MHz oscillator). The difference signal, centered at 50 KHz, is piped into an HP 3562A dynamic signal analyzer, which for the purposes of this discussion can be thought of as a very low noise FFT spectrum analyzer operating over the range 0-100 KHz. Mixing the DG-4102 output with a clean 10 MHz signal lets you magnify, in effect, the phase noise by an instrument with very narrow bandwidth operating at 50 KHz. The 3562A frequency span is set at 20 Hz, so each horizontal division is 2 Hz.
The first plot shows phase noise with the DG-4102's stock time base. Second plot shows the phase noise with the DG-4102 external time base input connected to an HP 3816A GPSDO. (I say phase noise, could be considered jitter as well.)
Quite the difference.
Rigol should have taken a leaf from Agilent's book and made an extra cost option of a high quality time base.