Are you trying to lower the noise or increase the stability?
Cooling it to sub zero and maintaining a stable temp will lower the noise and increase the stability but at a very expensive cost. A quality DRO will have a better stability and lower noise without going to the work of improving the geosat.
raising the temperature and maintaining a stable temp will increase the stability and lower the phase noise a tiny bit but probably increase the gain noise, but much cheaper. But still nothing a quality DRO cant outperform.
Quality DRO's can maintain 150khz stability easily, there are even some that are better. a DRO will always have a lower phase noise then a PLL. If you need sub 1khz stability (satellite tv can handle 100x worse no problem) then you jut dont have any options, and a PLL is the only way.
Its a fun project, but your not really going to see alot of gains for the amount of work your doing.
Now if you take a high quality DRO and cool that, now you can see some gains. There was an interesting article I read years ago, cant find it anymore, I think it might have been in tele-satellite about cooling a DRO
UDL