You can tell when it has been a good Arc by the welcome the winner gets on return to the paddock canopy of les platanes. Outstanding horses get a rocking reception by a crowd of racecourse wildebeest stampeding to get a view. Those who accomplish less stirring deeds - such as Carnegie and Urban Sea - come back to spatterings of polite applause, the sort of noise you get after a pianist's effort in a hotel bar.
And it is with Carnegie and Urban Sea that Sagamix has been stapled by Timeform. Urban Sea, according to the Halifax-based handicappers, is the only Arc winner of the last decade who was inferior to Sagamix and even she, in theory, would not have finished behind him thanks to the 3lb allowance for fillies.
The grey's rating is likely to settle at 129, compared to the 137 of Peintre Celebre last year and Helissio's 136 the season before that. Lammtarra's mark was 134. In addition, Sunday's time was woefully slow.
"On similar ground, Helissio was four and a half seconds faster," Chris Williams, the senior Flat handicapper at Timeform, said. "Lammtarra was on dead ground as well and he was two and a half seconds faster.
"They ignored the pacemaker [Happy Valentine] and it was not a strongly- run race. Consequently one or two were left with a bit to do and didn't get the best of runs. I don't want to knock an unbeaten Arc winner, but if it had been a more truly-run race High-Rise, Dream Well and Croco Rouge would have finished a bit closer."
A form problem is the proximity of such as Caitano and Fragrant Mix (the fifth and sixth), horses which are more yardsticks than active contestants at the highest level.
Britain's poor response to the Parisian challenge can be gauged by the fact that not only did France manage to get two horses home before the leading pair from les rosbifs. Germany, the equine tiddlers, also managed to do so.
In addition, the British standard bearer, Leggera, will surely not go down as the leading athlete in home competition this season.
Connections were genuinely stunned by the filly's level of performance. The Arc was considered out of Leggera's ability range for much of the season, which is why she had to be supplemented in the run-up. She is still improving and is clearly a runner of distinction on soft going, yet there are not many judges who do not believe that Swain, for example, could beat the filly by more than a neck.
There has not been much brio either about Sagamix this year. He does not run nobly, but rather flat and close to the terrain, like a lizard darting for the sanctuary of a rock. The colt's victory was more of a billboard for his sweating jockey, Olivier Peslier.
Peslier is on his way to becoming the most celebrated Arc jockey of them all, as he closes in on the record four winners of both Yves Saint-Martin and Pat Eddery. Only the foolish would now say he does not belong in their company.
Cerebral rather than physical accomplishments characterised Peslier's previous two victories in the race, when Peintre Celebre and Helissio were allowed to express their manifest superiority. Sagamix was different and more difficult. Such were his partner's powers of galvanisation that it is possible Peslier would have won on Leggera as well. He was the strongest man out there. Indeed, the Frenchman might even have won the damn thing on his Derby-winning mount, High-Rise, who was back in seventh.
Michael Kinane will draw no great joy from the ride he gave High-Rise. Luca Cumani, the colt's trainer, can at least comfort himself that he kept wise counsel when an obvious outlet would have been to blame his jockey. What must have been overpowering disappointment settled behind a smiling mask. Three months of preparation had been neutralised by one of the less judicious performances of Kinane's well-rewarded career. "That's racing," Cumani said to us. "That's a cock-up," he must have said to himself.
We will see more of Peslier this weekend, when he returns to Britain at Ascot, principally for the Princess Royal Stakes. He won the race 12 months ago on the same filly he rides on Saturday. For a man who showed so much brawn at Longchamp to go with his undoubted brain it is perhaps apt that Peslier's mount is Delilah.
The Queen's trainer is forced to give up, page 5