I've owned a Clavinova CVP307 since 2006. I did have a DGX but don't remember what model number it was. In my opinion with my experience with the 307 vs the DGX, there's no comparison. Not sure about the models you wrote about because I have never played either of them. At least the DGX action was closer to an arranger touch/action versus a piano.

As far as the CVP 307 it has Graded Hammer 3 (GH3) the key itself is made of wood with a synthetic covering. the GH3 swings back faster, like high quality piano keys. GH3 allows the player to feel the weight of the key when depressed a second time, even when the player has not completely released the key after the first push of the key and also performs as fast as an acoustic grand piano. Do a wikipedia search for the Clavinova it has some great info there.

The sound system of my 307 is far superior than to what my old DGX had:

Amplifiers and Speakers

Amplifiers 60W x 2 + 20W x 2
Speakers (16cm + 5cm + 3cm (dome)) x 2 + 10cm x 2

Here's a link to the CVP 307 now discontinued:

http://usa.yamaha.com/products/musical-instruments/keyboards/digitalpianos/cvp_series/cvp_307/

Another link below to a review posted by Tapas a SZ member, the thread is from 2004. Note his comment #2 about the CVP 307 and 309 comparing keyfeel/touch similar to a Steinway.

http://www.synthzone.com/forum/ubbthreads.php/topics/131535/Yamaha_CVP_307_First_Impressio