OK
Here's the method I used to bypass the locks on my 4770's
ATI Radeon HD 4770 Video Card Overclocking Guide - How to Overclock The Radeon HD 4770 - Legit Reviews There has to be something similar for the 5850's, some of the clocks they're being limited to are pathetic, I saw one card that was limited to 775/1125. The Asus BIOS will allow for 1200/1400 but flashing the BIOS tends to void the warranty with some companies.
The clocks of each card can be set seperately and really you should find their maxes seperately. However when you bring both cards together in CF you'll probably find you can't get quite as high clocks on each card as you could with only one installed. Running something like Furmark to stress the card after each tiny adjustment is also a good idea. Avoid using the CCC's Auto tune feature at all costs.