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I have tried running those YTOs past 10 GHz, and what happens is that they
just stop oscillating beyond a certain point (about 10.3 GHz as I recall).
If you bolt the oscillator to a good thermal sink and keep an eye on the
temperature it will probably be safe enough... but whether it will still
oscillate is another question.

I'd be interested in hearing how things go with the sampling phase detector.
Conversion loss at high harmonics, and the resulting need for lots of IF
gain, can really eat your lunch with those. From what I've seen there is no
longer much upside to using harmonic samplers over modern PFD chips. The
best of the Analog Devices parts (ADF4108, about $7/ea.) will work at Fin=8
GHz and Fcomp=100 MHz. You can't run either of them at N=32,000 and expect
miracles, obviously.

Obligatory HP content: I spent a lot of time trying to clean up my 8566B's
first LO synthesizer before I realized that the conversion loss of the YTO
sampler was never going to let me do better than about -105 to -110 dBc/Hz.
The low effective N factor rules out the ADF41xx series PLLs in that
application, but I think I could have gotten into the -120 dBc/Hz range with
a Hittite HMC363/HMC439 combination if my motivation hadn't run out.

-- john, KE5FX