But there is a DEMO Download with sample applications that run very very smooth.. but I guess you knew that and you're looking for a try-before-you-buy thing. well, consider this - If you like the DarkBasic Classic Demo - then You the same stuff in DarkGdk - but in a arguably better programming language and definately get faster programs - unless you write code so poorly it doesn't matter...which I doubt!
So - forget the demo - anti up - fire up the DarkGDK help file, google, and your compiler - and start making a game!