the runes work on a 10 10 8 8 8 8 sec cool down methed so if you could use all runes one after the other in 2 sec period the first rune would be 10 sec cool down and same with sec but the ones after it are 8 sec . which means they refresh at the same rate. Read this in a DK forum post with supporting evidence. Still not sure if its true but i know castsequence macros work well i have Nax25 and ulduar 10 gear and can pull 4-5k dps in 10 man with a castsequence macro as solo .