Honestly I think in many areas the WK is above the DGX-305. Especially the newer WK-3700. The DGX does not have voice editing, no modulation wheel, (crappy pithbend wheel), distortion guitar and bass sounds don't even compare to the WK.
The newer WK's have new piano samples (which I think are as good if not better than the DGX. The WK is also going to give you a better speaker system with more bass and crisper highs (because the WK's tweeters are better)
Plus the WK will let you load in new samples. Using the included software you can convert samples to the Casio format and use in the WK. Oddly enough I use my WK's sampler memory to trigger (live railroad sounds for my model train layout)
If I'm correct (not sure off hand), but I think the WK's going to give you more song editing control (after the recording is completed).
Overall I think the WK's more bang for the buck. Sure Yammie has those signature voices, but the preset voices on the DGX (in my opinion) are well below the WK-3500/3700. This I think is also because the WK's effects are (MILES) ahead of the DGX.
I got to play the DGX-305 about a week ago while out of town, and like before I was not impressed. The only sound on the board that made my mouth water was the "sweet saprano" sax. Gotta give it to Yamaha because they really NAILED that one.
The store I played the DGX in also had a WK-3500 sitting right next to it, so I and the sales rep were doing a side by side comparison. Man, I'm telling you the distortion guitars and bass quitars on the DGX are a joke! You can't do any serious pitchbend work because the quality of the wheel is quite poor. The piano's were up in the air. I think after dropping the reverb down a bit on the WK-3500 it faired VERY well against the DGX.
If you can try both models out for yourself. Hopefully you can find a store that has both
Squeak