I don't know much about DGDK but I looked around and found a few things that might help.
1)Dark GDK is faster then DarkBASIC. That is what it says on the site at least. The main difference is that Dark GDK uses C++ programming while DarkBasic uses a form a BASIC(I think) You should check here
http://darkgdk.thegamecreators.com/and here
http://darkgdk.thegamecreators.com/?f=darksdkvsdbpro for more inforation
2)there are not nearly as many users for Dark GDK as there are for DarkBASIC but there should still be good support for it but you should probably try posting on the Dark GDK board found here
http://forum.thegamecreators.com/?m=forum_read&i=22
I have never used Dark GDK so I don't know how easy it is to learn or use.