On the eve of the final stage on the Champs-Elysees, the seven-time champion told The Associated Press in an interview that he did as well as could be expected. He offered high praise for his Astana teammate Alberto Contador, who is headed for his second Tour title.
Armstrong said Saturday that even at his peak from 1999-2005 he might have lost to his Spanish teammate.
"Contador is that good, so I don't see how I would have been higher than that," he said.
Armstrong returned to the Tour following a 3 1/2-year retirement with the goal of drawing attention to his campaign to fight cancer, and to quiet the critics who doubted his seven Tour titles were doping-free.
The 37-year-old Texan was second at one point this year after missing the yellow jersey by a fraction of second, but heads to the ceremonial finish in Paris on Sunday in third place.
Of 26-year-old Contador, Armstrong said: "I think his performance this year would have beaten my performances in '01, and '04 and '05."
He added that the Spaniard was even better than Jan Ullrich, one of Armstrong's biggest rivals during the years that he won the Tour.
"Absolutely," he said. "Far better."
Armstrong, however, expects to perform better in 2010, and perhaps even beat Contador.
"I'm staying positive," Armstrong said. "My level will be a little better next year. If he has the same level next year that he has this year, (it will be) difficult to beat him. That's just a fact, a scientific fact."
But Armstrong expects to come to the Tour with a strong team, including current Astana teammates Levi Leipheimer and Andreas Kloeden, and together they could challenge Contador.
"There's a lot of variables there," Armstrong said. "My condition, his condition, team tactics, tactics of the race. … But that's why we do the race, so we know."
Aside from his crash in March when he broke his collarbone, Armstrong, who is expected to ride the Tour next year with his new Radio Shack team, said he is happy with the way his comeback has turned out.
"I wouldn't change anything about my performance, the tactics, about the preparation," he said during the interview in his hotel room. "Sure, we'll change some things next year, but looking back at this season, we did everything we wanted to do."
Before Sunday's final stage — a largely ceremonial ride into Paris, Contador all but sealed his second Tour de France victory by keeping the yellow jersey after Saturday's punishing stage. Armstrong remained in third overall, 5 minutes and 24 seconds behind.
Asked about his plans beyond 2010, Armstrong answered that he would still be involved in the fight against cancer and in cycling.
"I mean, the two passions in my life, aside my family, are cycling and cancer," the cancer survivor said. "And I've got to stay involved in both of those. My life needs those things. And, I think, those things need me."
Following his last Tour victory in 2005, Armstrong railed against the "cynics and the skeptics" who believed his triumphs were tainted by doping.
"There was a ton of doubters, and a ton of critics, negative people in the press room, I was sick of that. They are still there. I don't think they are as many as they were, but they are still there."
A month after his retirement, L'Equipe sports daily reported that Armstrong's "B" samples from the 1999 Tour contained EPO — a banned blood-booster. Armstrong insisted back then that he was the victim of a "witch hunt," and a Dutch lawyer appointed by the UCI later cleared him.
Armstrong said his third place on this year's Tour could help silence his doubters.
"If you are on a fence and you are objective about it, and you look at a 38-year-old athlete, tested 50-plus time this year, more than anybody else. … The only thing you can say is you have a super secret mystery drug. …"
He then dismissed his doubters with a profanity.