Quote: "although there is a slight performance drop with the DGDK.NET version purely because of the nature of .NET and the Interop layer"
correct, because there is a COM Interop layer between the base code and the .NET environment. If and when TGC decide to do a full .NET port of their base code, you can expect speeds equal to or slightly better than c++ (not including known issues with performance degradation in both c++ and .NET languages, like 2d for example)
At any rate, if you prefer c++ then get the dgdk, if you like vb.net or c# then get dgdk.net. If you have some basic skills in c++ and want a friendlier version of it then c# (dgdk.net) is perfect. Plus, with dgdk.net your not limited to just the c# flavor, you can always try out vb.net which is good if you come from proceduaral BASIC like dbp, then you need only learn the basic concepts of OOP to get off the ground and start running. All depends on your past experience, and where you want to go.