I've been using a pretty old third-or-fourth-hand HEQ5 (not modified) for about two and a half years now.
Was pretty happy with its performance until I switched from 432mm AT72EDII to 1370mm RC6.
Without a reducer at native 1370mm, the guiding was often not good enough with HEQ5.

I just acquired a barely used CEM40G to replace the HEQ5.
Like it so far.
It's actually quite hefty - just a little lighter than HEQ5. But the allowed payload is almost 50% more.
The guiding is great. Over two nights in my Bortle 8 yard I am getting 0.4-0.6" RMS total (as opposed to 0.8-1.8" with HEQ5).
(guiding with ZWO 30F4 scope and ASI120MM-mini)
I think I am going to keep the CEM.

There's a gripe about the CEM, though.
That's iPolar and iGuider.
These two things add about $500 to the price of the mount but do not work under INDI/Ekos.
iPolar I don't care much - it's redundant these days. Shame on iOptron. I would rather had a regular/optical polar scope or none at all.
iGuider - I really wish it worked in INDI/Ekos environment. Really. Please fix it. Thank you.

Thanks!