but I couldn't help but think that the Vixen QC might not be any better than the Synta.
The QC might not be better, but the Q definitely still is. You seem to be most interested, in this thread, in finding a mount that can give you a smooth PE that will be easiest to guide out. The Vixen mounts are more likely to deliver this than the chinese imports (at least so far as I've known, though things are changing very rapidly these days!).
I recently upgraded an old Super Polaris mount with an iOptron Gotonova goto kit, and so far I'm pretty happy with the results (and it was CHEAP to do!). See
My thread on goto'ing a Super Polaris
I once compared the PE on all my mounts using Astro IIDC and a firewire camera. The results were interesting.
My old super polaris had a very smooth PE of about 20-22 arc seconds. So smooth that it was easy to take 2 minute unguided exposures with a 4.25" f/5.5 Newt and have more than half the frames suitable for stacking.
My ~1980 vintage C-8's spur gear drive was also around 20 arc seconds PE, but very jumpy and non-periodic. Too long a focal length to image unguided, so I never tried. But I did try once to image with an SBIG ST2000XM and an AO-7 (WAY out of balance, so I only shot toward the meridian and zenith during that test), and the AO-7 gave round stars in exposures about 5 minutes long. No guide port, though, so I haven't used the old fork mount since that experiment.
Tak EM-10, Temma 2 Jr: This is truly a wonderful "light to medium duty" mount. I routinely mount the C-8 on it with a Megrez 80mm piggyback and take astrophotos with it. PE tested out to right around 8-10 Seconds as advertised, and is very smooth.
Tak NJP Temma PC: Wonderful moderate-heavy AP mount. I bought mine used for about $4500 about 3 years ago (paid about $2200 for the EM-10 at the same time). This mount doesn't care about winds that often kick up at my dark sky site, though I've only taken dark sky images with short tubes, like the C-8 with various refractors piggyback or on a Triad bar. PE right around the advertised 4 second level, and very smooth.
I would think that a used Vixen mount, perhaps a GPDX or some other derivitave of the polaris, and perhaps with one of the modern goto upgrade kits, would not steer you wrong, though your 9.25" would be at the upper limit for comfortable AP.