CDR Itemization and Runes

After coming back from a 9 month break, I was pleasantly surprised with the amount of CDR itemization options that are available. More importantly, I really like the new Black Cleaver. it gives a whopping 20% cdr. With so much CDR, my CDR runes seem obsolete. So, for bruiser champs like riven, pantheon, jarvan, and urgot, is it worth it to keep that extra flat CDR even though I'm probably gunna overshoot 40% with youmuus AND BC AND some defensive item.

Should I go youmuus AND BC or EITHER OR? (For Hydra bruisers, I'm probably gunna get SV or Frozen Heart for Urgot)