For the longest time the HZs have peformed admirably and the newer batches have also turned in excellent performance (DDR1100 and beyond).
The Ballistix line includes the 8000s and the 8500s, and since all three (including the 6400s) usually carry the D9GMH chips, it would make sense that the better chips in the Ballistix line are going to the higher binned modules. Granted, the 6400s still clock but pretty good and regulary run over DDR1000 and some even DDR1200, but I might be inclined to go with the GSkills if looking for high clocks at good timings.
If looking for good DDR800 perfomance, then choose the better priced set, which would be the Ballistix right now ($70 at the egg, after $45 MIR).
The Ballistix PC2-8000s are also on sale at Mwave ($88, plus shipping, after $40 MIR).
Both of these Ballistix are 2 GB kits, of course.