Their tales of the tape are almost identical but it is the improbable size of their competitive hearts that has become so compelling.
Just half an inch separates the taller Jamie Roberts, 6ft 4in, and at close to 17st he is just a few pounds heavier than the man who owns one of the most ferocious spirits ever bred in the Basque country, Imanol Harinordoquy.
This, however, is the least stunning of the symmetry between the two men who stand above all others when you try to separate Wales and France on what seems so likely to be the most decisive dividing line in the first of the World Cup semi-finals here at Eden Park, Auckland, in four days' time.
We are talking here beyond the huge and implacable physicality represented by the 24-year-old crash-ball centre from Newport and the No 8 who, while seven years his senior, produced one of the great individual performances in rugby history in the defeat of England last weekend.
We are considering a search for an edge, an all-enveloping authority of action, which if transferred to a boxing ring would undoubtedly be described as the War on the Shore.
Just as Shaun Edwards, Wales' brilliantly acute English defensive coordinator, has identified Harinordoquy – and, not so far behind him, biting full-back Maxime Médard – as the Frenchman most committed to the idea of winning, France have piled so much of their World Cup bounty on stopping Roberts.
The French centre Aurélien Rougerie yesterday said, almost as an aside, that he considered Roberts the best, most compelling figure of his own trade.
He said Roberts carried the threat of perpetual aggression. Then he reflected for a moment before adding: "His team moves forward every time he touches the ball. He is the centrepiece of his team. People ask why these young Welsh players are making such impact here, why we have to consider the challenge they represent so carefully. We have to start with Roberts because in his case it is so simple."
Harinordoquy (above) has enjoyed that status for many years, of course. Last year he was the northern hemisphere's only candidate for world rugby's player of the year, and some were not so sure that justice was entirely served when the winning vote went to the iconic All Black flanker and captain, Richie McCaw.
Yet for all the certainties of his nature, which made him a brilliantly combative sportsman in various disciplines, including the Basque speciality of pelota, before driving him away from the family business of cattle trading into professional rugby, there have also been the squalls of temperament that have not always made him a coach's delight.
A great man, yes, an uncomplicated one, no. Except, that is, in the matter of his extreme antipathy for the idea of ever again being beaten by the English. "Why do you hate the English so much?" he was asked in his youth.
"Because they are English," he said with hardly a hint of a smile. More than anything, though, the dislike has been fuelled by two unbearable defeats, both in the semi-finals of the World Cup, in 2003 and, worst of all, in the theatre of war he has made his own, the Stade de France, four years ago. "It is true they were terrible defeats and, yes, of course they stick in my gullet. They make me want to be sick," he said the other day.
Yesterday his coach, Marc Lièvremont (below), was looking much less like a man driven into a desperate corner. In fact, the apparent victim of a full-scale mutiny after the pool defeats by New Zealand and Tonga, was talking confidently of the new strength of his team's psyche after the mostly poised defeat of the English.
Not the least source of the new serenity – after announcing an unchanged team in which the only slight injury doubt is scrum-half Dimitri Yachvili – is the sense within the French camp that he scored a masterpiece of motivation when keeping Harinordoquy on the bench for the All Black and Tonga games.
"The coach was counting on Harinordoquy coming into the England game with a huge point to prove," said one French insider. "Lièvremont knows Basque pride and the anger that comes at any slight to it and the kind of motivation that provides. It was a great performance from Harinordoquy – maybe decisive in the way it set the tone. It may just have changed everything as far as this campaign is concerned."
Certainly, it is not so easy now conjuring the picture of a France enduring one of its worst bouts of disarray since the retreat from Moscow – and last summer's disaster at the World Cup of football in South Africa.
Médard, the full-back of nerve and panache so admired by Edwards who punched in the try that went so far in delivering England's death sentence at the weekend, talks of regained passion and confidence. "We had a bad time, yes, but I believe we are in the right mood to avoid any complacency after beating England," he said. "We have also beaten Wales in our last three games but we don't need telling that this young Welsh team has grown very strong.
"They will not be easy but you know we have a very strong desire now. It is to show a new facet of French rugby – our ability to be more consistent."
Yet if Lièvremont has the demeanour of a man just released from the Bastille there is also, and perhaps hardly surprisingly, still a certain caution. "It is necessary to remember that victory can, like defeat, sometimes tell you everything and nothing. The point is that the England match is over – we have different opponents offering new dangers."
Indeed, the team's physical coach Julien Delore put it rather more sharply, saying: "The Welsh present new problems because they are so very strong physically and they play such fast ball. We knew what to expect from the English. They can be very strong but also predictable."
There is also the kind of doubt which can ambush even the collective will of Harinordoquy and back-row comrades Julien Bonnaire and captain Thierry Dusautoir, even when it is at its most intense and refined.
Rougerie, another Frenchman who was so possessed by the idea of driving away the English, had already suggested as much when he spoke of the depth of the Welsh challenge. He talked of the strength and the optimism of the team who seem to have learnt how to play without fear.
Then, before being ushered away by French officials who perhaps believed he had been candid enough for one day, he winced when asked if he and his team-mates were now safe from the kind of breakdown which came against Tonga and left them so close to flying home.
"No, we are not," he said, "we can still be driven by the demons who sometimes come to visit us."
It is his special prayer, you have to suspect, that this time they do not happen to ride on the back of Jamie Roberts.