You have to compare fight lenght etc. to make clear statements about procc rates. I sometimes see higher dmg% of the cloak for some shadows , but that depends on when the cloak proccs since , as far as i know , it scales with spellpower at the time it proccs.
It does scale with haste, if you mouseover the cloak you'll see the proc rate for your level of haste, eg at 50% haste I have 3.70 rppm.
And yes, lazu is correct the damage it does is based on spellpower, if you get lucky and have it proc while you've got 115k SP it'll hit like a truck. There's also the 5 target limit to take into consideration when comparing logs.
Nah this is just single target and the fight lengths are the same. Thanks guys, didn't know it scaled with haste. I was wondering if there was a way to game the proc since sometimes it procs back to back (to back).