honestly I get the sense that Benton is talking complete bs in his story that he was in on the filibuster plan and had gotten Mitch to give the green light, as it were... just sounds completely ludicrous. Mitch didn't even come to the floor until very late.
what it seems to me is that Benton floated this story because Benton's in charge of getting McConnel re-elected and wanted him to be associated with the hugely popular filibuster. the way Rand told the story is much more likely to me, I think he probably talked to Benton/McConnel about possibly doing a "filibuster" in the same sense that he had "filibustered" to force a vote on his foreign aid bill and all that which yes, kept everyone there until midnight on a Friday, but was nothing near like this. Rand didn't know he was going to do it that day, he got the floor while leadership's guard was down (not because Mitch had set it up for him in any way, that's Benton BS I think) and they thought he was just going to give a little speech like normal. if Mitch was so supportive he'd have come on much sooner I think.
other than that, Rand's working relationship with McConnel is absolutely essential to his strategy to be as effective as possible in the Senate.