Judging by the first test, the decision can be pivotal to the outcome. Bat well first, as Pakistan did in reaching 566 for three, and you put pressure on the other side which can magnify as the game progresses. Australia know it and New Zealand are realising it too, if Abu Dhabi was a gauge.
Those batting second, especially visitors in foreign conditions, need significant mental tenacity and technical nous to sustain parity.
McCullum wouldn't divulge his choice - in the UAE the 50c equivalent involves calling Arabic numbers or an oil refinery - but he was left in no doubt as to its importance.
"I'd desperately like to win it because it swings the odds slightly but if we are presented with the opportunity to bowl first [i.e. McCullum makes the wrong call], hopefully we can make some improvements from our last effort. The call won't necessarily be the difference between winning and losing if we find a way to be better."
New Zealand are expected to make minimal changes to their starting XI. McCullum confirmed he will open throughout the series. Swapping Jimmy Neesham for Luke Ronchi appears the only potential diversion from the status quo.
McCullum got his first chance to look at the wicket at yesterday's practice. The desert-coloured rectangle met the forecast of a local contact.
"He said it would be 'juicy' and I replied 'for seam?' and he said 'no, for spin'. It doesn't surprise me, that's what we expect in this part of the world."
Pakistan captain Misbah-ul-Haq defined it as "a typical Dubai pitch" which would be good for batting at the start, slow down and then turn later.
"Sometimes it can give you a big advantage to bat first, but in the second innings of our recent tests [against Australia and New Zealand] we have batted well on third and fourth day pitches. We're confident batting second even with wear and tear."
New Zealand have worked on deficient areas such as reverse swing and spin angles on the crease since the opening defeat but McCullum was at pains to point out they wouldn't be ditching their game plan.
"One of the dangers of such a tough defeat is you overhaul things which you don't need to. One thing we pride ourselves on is making subtle adjustments. Take the West Indies series when we lost heavily in Trinidad and responded with a match-winning performance in Barbados.
"Sometimes the only way of learning lessons is by getting out and confronting your difficulties. That was one of the benefits of the first test. We now know how they attack [in practice] and we've worked on a game plan to counter it."
New Zealand will face one and possibly two different Pakistani openers. Ahmed Shehzad, a batsman McCullum said "sucked the life out of us" in Abu Dhabi is ruled out with his minor skull fracture while Mohammad Hafeez has a hamstring problem. Taufeeq Umar played the last of his 43 tests in 2012 and averages 38.72, while Shan Masood played twice against South Africa more than a year ago, including an innings of 75.
Misbah was not worried about how they'd fit in: "Masood played well against South Africa and Taufeeq is experienced and middling the ball well. These two are good enough to give us a start, depending on whether Hafeez's hamstring recovers."
- Andrew Alderson of the New Zealand Herald
