McCullum pointed to his side's progression every match as the most pleasing part of the series.
"We have been able to continue to raise the tempo of our game and to execute better each game that we've played," he said. "We've still been able to, when we cross the line, be pretty emphatic in our performance."
The improvement with the bat today - by one run - was thanks in large to the captain's own blazing innings.
New Zealand had 150 on the board when McCullum arrived at the crease, and when he was out on the last ball of the innings for 119 from 88 balls, the intrigue was all but over at the intermission.
McCullum described his knock - the No 4 was sedate at first before unleashing in the end - as a result of circumstances.
"Losing two wickets in a row meant I had to try and get settled. Then, when we had the base, we were able to launch an attack towards the end, and that's when things hastened a little."
Martin Guptill and Rob Nicol again had New Zealand off to a rollicking start, and when the openers brought up 150 in the 22nd over the eyes of most fans were fixed on the record books. But just when the cricket almanacs were being cracked open Zimbabwe struck a double blow, with Nicol trapped in front for 63 and Guptill stumped for 85 the very next ball.
McCullum enjoyed handy partnerships with Jacob Oram (25), Kane Williamson (38) and brother Nathan (21 from 7), bringing up New Zealand's 300 in the 45th over. And after making the most of yet another grassed catch when on 48, he reached three figures to put his side well and truly in charge.
With the ball, a wicket on debut from left-arm seamer Michael Bates was joined by Taurn Nethula's first two for New Zealand as the highlights, while spinners Williamson and Nathan McCullum also picked up a pair each.
Aside from Brendon Taylor's well-made 65, there was little for Zimbabwe to shout about with the bat as they showed few signs of progress made during the tour. Their innings petered out tamely, though they may claim time at the crease will be of benefit when the two-match Twenty20 series starts in Auckland on Friday.
McCullum admitted that series was a chance for the visitors to take something from the tour other than wounded pride.
"We've played very, very good cricket so far. We've got two Twenty20s where I think the skill level, the gaps between two teams, is always narrowed. It means we're going to have to be even more efficient."