Cameron and Key have a lot in common. Both toiled for just four years as MPs before becoming leader - of parties long mired in opposition. Both of these fresh-faced compassionate conservatives attempted a kind of decontamination of the party image, positioning themselves very much in the modernising, easy-going centre - in some cases slinging a leg seductively over the left side of the bed.
Cameron travelled to the Arctic to hang with the huskies and declare himself a committed environmentalist. He hugged hoodies, claimed to be the holder of the "progressive" flame. Key, too, talked up green goals, conceding National had "taken too long to put the protection of our environment at the forefront of our thinking". And who can forget his lamentation of the plight of the "underclass" - "the shame of us all"?
Both now are struggling to live up to those oaths. Both have faced criticism for excelling at salesmanship rather than conviction. Both are accused of providing cover for parties permeated still by the same old nastiness.
Key may have his problems but they pale against Cameron's. The Tory leader is struggling with a loathed coalition partner, fresh internal threats from the anti-Europe wing, an independence-hungry Scotland and economic stagnation.
And then there's Boris. Buoyed by the Olympics, the London Mayor is riding a wave of "Borismania", as the Daily Telegraph put it. With the most recent poll giving the idiosyncratic but ambitious Johnson a popularity rating of plus 30 against Cameron's minus 21, many Tories regard him as a great blond lifeboat.
Watching from afar, Key could be forgiven for quietly thanking the universe that he doesn't have a Boris of his own to contend with. John Banks might have a Borisesque ability to surprise, but that's about it.
There is another striking similarity between Cameron and Key. Their wealth. Both entered politics as millionaires. And not just any millionaires - both are estimated to be sitting on fortunes worth more than $50 million.
But the means by which they accumulated that wealth betrays the biggest difference.
Key reportedly spoke as a boy of wanting to be a millionaire and prime minister.
Cameron achieved the former at birth. As we all know, John was brought up by a solo mother, in a state house. Had he enjoyed Dave's Etonian privileges, New Zealand's top job would surely have been much harder to get.
And while Key's years travelling as a currency trader might be regarded by some as a limited foundation for a career in politics, it is a broad pre-parliamentary hinterland compared to David Cameron - whose real-life experience before becoming an MP amounted to working for the Conservative Party and in PR.
Cameron might proclaim an "aspiration nation", but it is his New Zealand analogue who embodies it. As Cameron strained to turn his silver-spoon past into a strength this week - "I'm not here to defend privilege, I'm here to spread it" - it became clearer than ever that his text-pal John has one great, unreachable political advantage over him: a useful back story.
Toby Manhire is also a columnist for APN's Listener magazine.
