bro, derbi is more matchable to GS150 in terms of power and top end speed the reason why it is giving tough time to CG is that it has equally good maneuverability in street/traffic due to its short tail, small wheels, and less height.. thats where GS lacks due to its big wheels Big size which makes it less maneuverable...
About YBR, its too early say any thing about it (I am very hope full) but as we see its specs, I am afraid it will not be able to undo CG Curse any soon. Also about Price I am not sure what they are going to do with it.
Another thing which I came to know about YBR is that its being sourced by chinese sources, all those importers from china who feed RP125, GS150, GD110 have been contacted by Yamaha Karachi Plant to feed them with constant supply of parts from china.
So you can well imagine.
So Much for a Japanese Bike..