CoF worth the upgrade.
 

So currently my rogue has a RBG and Seb Cloak ( I know haste doesn't stack) and I'm debating on selling them both and buying the CoF. Would this be worth only a 9% increase in haste?

Yes, haste is one of the few stat that actually matters in this game.

more haste = faster backstabs.
its worth it. Also once you are done with it. you can sell it back.
Any Tradable upgrade is a good investment.

The only time a CoF wouldn't be a huge upgrade from an item with less haste is if you have an rbb & a monk epic.

Thank you for the input gentlemen!

Your epic is 40% haste but doesn't impact your backstab CD. When you get epic + 41% haste you will see a massive difference in your backstab cooldowns.

Yea unfortunately I won't be seeing a 41% haste item anytime soon. Currently my guild doesn't do sky ATM