Funny you've raised the issue just when I traded my D2x for a D300, and was contemplating a comparison of these two cameras myself. A few weeks back, I made a similar comparison between the GRD-2 and Kodak DCS Pro SLR/n and reached somewhat striking (immature perhaps?) results: Ricoh failed miserably in white balance (I was shooting RAW), and to add insult to injury, gone were the details of buildings I've shot from a couple of hundred meters. Kodak, itself not a good performer in the white balance category, excelled when compared to the Ricoh.
Last weekend me and my girlfriend went to some rural parts of Turkey with my new D300. She used the GRD-2 (Fine jpeg, b+w) and we nearly always ended up with similar shots. I liked her photos a lot, though I'm also much impressed with my output with the D300. A dynamic range almost comparable to Fujifilm S5 Pro, an attractive soft look without compromising resolution and detail, and lovely colours I've come to expect only from Sigma SD-14. A comparison would be unjust however, since I shot RAW only. Anyway, to sum up, I have a feeling that GRD-2 is best when shooting b+w at close range.
Will keep in touch if something creeps up. By the way, I liked your shots very much.