I encountered the same dilemma when I was trying to choose between the two versions, and I was actually leaning toward the RG version until I realized that the RG version does, due to the pink printed indices, look too "warm". After I purchased the PT version, I got to see both versions side by side and that impression was confirmed. In contrast, the RG Datograph looks (at least in pics) much cleaner thanks to the contrast of the silver subdials and white print against the RG.
In contrast, the PT version is very cool and clean, sort of like a winter evening. Also, the PT version has the beautiful polished/brushed case sides that all RG Lange watches lack.
All that being said, it ultimately is a very subjective question, as Thomas and many others have praised the warmth of the RG version. Just a matter of what you are looking for in a particular watch.
P.S. Thomas, I was wondering why the RG/black dial Sidestep looked so good in your pictures, until I realzed that it precisely because the white indices that provided a nice contrast with the RG case.