I have been absent from the astro imaging world for a while now, but recently decided I would make an investment into some larger gear to chase down some closer fields.
I ended up with a GSO 12" f4 truss scope from Paul Haese, and with the help from Bintel, I have it mounted on a CEM120 on a tripier 360.
Guiding with my lodestar and OAG I am really happy with the stability of the setup. Forgive the gradients, imaging luminance from my house is not the best idea, but I just wanted to shoot something to tune out tilt. Currently I am using an old MPCC MK2 and I am not 100% happy with its correction, so I have a GPU coming along with some adaptors to thread it to the focuser.
By virtue of only having one of them, I couldn't really tell you. So far the CEM seems pretty good, holds my 12 inch pretty happily, and my only real gripe is that the software control is a bit clunky.
Being that I don't really need to control it too much (SGP takes over after alignment) its no big deal.
The CEM mounts seem to like the PHD2 PPEC algo for RA, give that a try and you might find it performing even better guide wise. If using that the other advice is to fix PHD2 to the natural worm period (240 secs for a CEM120?)