I have a CT129N, go for the CX600! When I got the CT129N, it was the only & biggest 'bench-top' column style mill\drill available, 3/4HP motor, MT3 Spindle. The CX600 has 1HP motor & R8 Spindle.
Also, don't bother with the 'stock' stand, although sturdy, it's too short and 'nil' for storage. I got the 'Grey' 95408 side rider, the 18" x 18" foot print is perfect, as well, the side cabinet will be perfect for any DRO\CnC electronics upgrade. The stock stand (in my case) was part of the sale price but now is a perfect grinder stand!
I also added about 200Lbs in angle, channel and plate steel, (IMHO when it comes to 'Milling', the more rigid\massive the better,) as well as the 100 or so pounds of tooling in the drawers.
If I was doing this again, I'd definately get the CX for a 'bench-top' mill.
That's my I-wish-the-CX600-was-available-four-years-ago opinion.