Need dual link DVI mini displayport cable for Cinema HD to work well

Looks like if you use a DVI mini displayport cable with a Cinema HD display then you are limited to native macbook resolution. The cable works fine with a 24" display, I get 1650x1080 with that. It also works with my 1080p TV at 1920 x 1080. But, all I can get with that cable and my Cinema HD (30") is 1280 x 800. I'll buy a dual link cable over christmas to try to see if I can get a 2560 x 1600 display working.