GDL 0.9.1 compiled from source for OpenSUSE 11.3 64 bit gives slow loops and where execution relative to IDL 8.0.1.
See attached program for example code. On my server running sw, 1000 gives the following times:
GDL: loops=1.03 where=0.0686
IDL: loops=0.146 where=0.00313
The results are the same so GDL agrees with IDL so that's good but the speed of execution considerably slower in GDL.