I think people are throwing Overeem out of the picture a bit too early.
He was quite easily defeating Bigfoot the first two rounds, more than once he tossed Bigfoot out of the way/down like a child, he didn't even look like he was trying in that fight. He got really cocky and paid for it, but I highly doubt he will do the same against JDS.
Overeem can definitely beat JDS if he plays it smart and is in top form.
With that said, Cain is going to destroy Bigfootagain, and even though Overeem CAN beat JDS, I think JDS will pull it out.
“Anna, my strong, terrifying Anna.” -Cas
"You lack the testicular fortitude to study under me" -Elodin
“slow and drunk is no match for fast and scared shitless.”-Jacob