Armstrong is definitely stronger on the moutain but Indurain even if he could, he wouldnt break away and leave everyone behind. He normally had a big time advantage once the mountain came or he knew he would make it up on the ITT. Many times he could have won or step up the tempo in the climb but he usually never did it and many many times he let the other guy take the stage - like Armstrong did with Basso (but without saying he let them win). He didnt have the take it all approach that Lance has, so he saved himself in the mountains, i dont think we will ever know how good he could have been there.