Never used a CGEM Pro, and I am still saving to buy a CCD imager to use this my CGEM: so can't help too much. Next tax return time I will get a camera.
I am impressed with the quality of the CGEM and I bought it at the best time ($3500 for the CGEM 925). I deliberately bought the 9.25" to make sure it is running well within its weight range when I image down the track.
I am also running on a tight budget, so I was very careful in trying to work out what I wanted and how best to get there. I got the CGEM 925 since it was portable enough (I don't have a permanent site) but should deliver good performance. I didn't want to get more than one scope - I wanted a jack of all trades - visual observing, imaging, portability, etc...
So far I am very happy, although the normal Celestron SCT OTA take a long time to cool. The HD are much quicker than the standard OTA for cooling.