Sorry for the rubbish pictures but this is all I managed with a loupe and the iphone in "freehand mode". The different light play in the dials can also not be shown with these photos, but this has for me the biggest influence on how the dials appear in natural light, with the watch on the wrist.
The work of Jochen Benzinger shows sharper "ridges", particularly towards the centre of the dial. Since he is using silver for the dial blank and only puts a very thin clear lacquer on the finished dial, the pure silver coming up through the frosting leads to a very delicate sparkling. But for some reason there is much less shadow play compared to Kari Voutilainen's dial, which could have something to do with the different forms of the "corns" in the pattern.
The guilloche of Kari Voutilainen is stunning by its extreme precision. When we discussed his GMT watches recently, we run out of time before assessing my watch, so I am not yet/no longer sure how the surface of this dial is treated. It is based on a gold blank, so the "silver" is either painted or brought on by a galvanic process. This silvery-white colour leads to such a strong shadow play that the initially planned finer pattern had to be given up, otherwise the dial would have become too busy. While this dial also has a faint silver "sparkling", it is not in the same irregular and more natural way visible as in the Benzinger dial. When directly comparing the two dials, the Benzinger one leaves generally a more "artisanal" impression. Viewed as a whole, I believe these different appearances of the dials of the two watches have exactly the right "touch" to fit in with the detailing of the rest of the watch: A more artisanal touch with the Benzinger, absolute precision with the Voutilainen.
Taking in the PP 5930 to compare, you lose all shadow play with a darker dial colour. The guilloche pattern has thus to be more intricate to attract interest. As nicely as the guilloche work is done on the PP, it looks a bit "industrial" to me compared with the other two watches. But you could say, this is again what is required for a coherent look of the watch.
Many thanks, Magnus, for sharing your thoughts. Commissioning a watch with a one-off case brings such an adventure indeed on a completely different level if not an almost generic shape shall do. But when a "unique piece" (including movement changes) is based on an existing model, getting involved in the creation process with its direct exchanges with the master watchmaker, the issues arising can be well managed (including finances) and bring an unforgettable experience with it. The GMT models in Kari Voutilainen's range have all been developed based on an initial commission of a customer. If you have a good idea for a complication, there is thus always a chance that a new model an independet watchmaker is developing and later offering is exactly what you want.