I also have Ballistix z503 and G.Skill HZ 2GB kits. I haven't had long to play with the G.Skill, but have already found that the Ballistix is superior in this board and that my CPU temps are slightly higher with the G.Skill.

The Ballistix is just unbeatable 1GB RAM (when it's good) and I think that's reflected in the price differential with the G.Skill.