Undoubtedly their combination benefitted from also playing together for the Hurricanes and that's where Smith could be vulnerable.
Meanwhile, Nonu has been playing non-stop without a decent break since this time last year. By June, he could be running on empty.
Even if he keeps fatigue at bay, Nonu will have Sonny Bill Williams casting his considerable shadow over proceedings.
The Chiefs second five appears to be in a good space - settled in Hamilton and more willing to attack the line and back himself.
Seeing how Williams' combination develops with Kahui will be fascinating.
So far they have been sporadically effective together without a definitive performance.
They make a supremely physical proposition and yet both players are compelling selections in their own right.
Kahui has taken just four weeks to establish himself as probably the best defensive centre in world rugby.
Against the Highlanders in week one, Ellison had his hands on the ball all night, but as much as he twisted and turned, he couldn't lose Kahui.
Agile and aware, Kahui is rarely drawn out of position but he packs a more explosive punch than Smith.
Kahui has the power to bury people and make a statement on defence, and in a test match, that can be critical.
Former All Black backs coach and current Chiefs technical director Wayne Smith has little doubt that Kahui will again force his way into the test picture but may continue to be used on the wing at that level.
"I thought he and Cory Jane were the two best wings at the World Cup," says Smith.
"I don't think there is any issue with him continuing to play centre and wing. I like him in that dual role and I think there is a lot of compatibility in skill sets.
"He's so good under the high ball, he's quick, reads the game well, tackles hard and I would even rate him as one of the best kickers off either foot. I think we'll see him as an All Black wing again this season."
Whether Kahui spends more time at wing or centre with the All Blacks may depend on the selection made at No 12.
It's logical to play Kahui at centre if Williams is in at 12, but on the wing if Nonu and Smith remain the preferred midfield pairing.
THE PICTURE could be complicated further if Fruean can sustain his form for the entire campaign. The 110kg Crusader is an astonishing sight in full flow. He had magic moments earlier in last year's campaign before fading.
The All Black selectors tracked him hard in the first half of Super Rugby, as they were taken with his destructive abilities. Ball in hand, attacking the line, Fruean was almost unstoppable.
The downside, however, was his work rate. In between bursts, he was deemed to be lazy, not working hard enough on defence or to get himself involved in the game.
That may have been a legacy of his 2010 campaign, when he struggled physically to last the 80 minutes.
Fruean had major heart surgery in 2008 after being diagnosed with rheumatic fever. When he joined the Crusaders in 2010, he was short of conditioning, having not attended a major rugby-playing school and also having been unable to train for the better part of a year.
There was a feeling last year Fruean may still have lacked confidence in his ability to play 80 minutes hard out and his goal in 2012 is to stay more involved in individual games and to maintain his form and impact for the whole campaign.
His power and former combination with Williams are strong reasons to include him in an All Black squad, and with Ellison, a one-cap All Black in 2009, also back, Smith will be under unprecedented pressure to retain his spot.
Ma'a mate
* Of Conrad Smith's 55 All Black tests, 35 have been played in tandem with Ma'a Nonu.
* Seventeen of those tandem tests have occurred in the past two years.
* Smith has scored more test tries - 11 to 10 - playing with other second five-eighths.
* Many of those 11 were scored in All Black try-fests against the likes of Portugal, Samoa and a weakened Ireland.
* Smith has scored most of his other tries (three apiece) against Australia and South Africa - all with Nonu in attendance.
* Smith has 21 test tries - 13th on the All Blacks' all-time list.
* Nonu is 12th, with 22 test tries.
