riven keystone

I used to do thunderlords a lot, but the extra 5% cdr doesnt mean too much to me..I mean... its just 3 less seconds on ult and .5(i think) seconds on e. However, fervor seems better because i can get the armor pen mastery along with the fact that riven can get 8 stacks quickly with a q a q a q a, and after that you can move on to another person(say if you were ganked) or if you were in a teamfight. With those 8 stacks you do a TON more damage than just a quick burst every 20 seconds, which is thunderlord's effect.