Re: 7 Stringer.. considerations
Haven't played the RGD, but judging from the specs it must be really great. I have an RG1527 (swapped the pickups for more clarity and output with a Q-tuner(n) & D-Activator (b)) and it feels awesome. Since the RGD's neck is prestige, it must feel great too. The longer scale shouldn't be an issue as I have relatively small hands and adapted in no time on my RGA-8 (27"). You won't have to use thicker strings, because the longer scale helps to maintain tension in lower tunings. So no stress! It also adds to the clarity.
If you're into low tunings go for the RGD. As far as the split coil issue, can be mended if you just change the pickup selector (and the wiring).
If not, the RG1527 is an all-around weapon! And 600 euros for a mint prestige guitar is really great.
I think that in both cases you will have to change the pickups though...
If you come down to choose between the RGs (considering that black doesn't bother you), you should know that a lot of guys here like the RG7620 better. I won't say that the RG1527's neck is better, I will just say that it feels different and I personally like it more. But the 7620's pickups are DiMarzios and far better than the 1527's.
The 7620 sounds a better purchase (if it's mint and at the same price range as the 1527).