As it was already stated, Suzuka was top of the class in the Knightmare simulation and the fact that he can achieve such a high sync rate with Lancelot proves that he is really one of the best pilots there are as the best are those who can unlock those potential.
If Karen was at the academy no doubt she would produce similar results. Lelouch picked her to be the pilot mainly because she is an ace pilot and can bring out its fullest potential.
Jeremiah and Cornelia demonstrated similar lighting fast moves in combat against Karen as well but failed because they were either surprised or ambushed.
My point? Their all good damn pilots.
Karen seems more of a berserker though, given the way she fights with the Guren and her screaming.
Sad though that 3 members of the student council were fighting in the same battle. Even worst that two of them are best friends. Even ironic that the best imperial pilot is a Japanese while the best Black Knight pilot is a Britannian (Also half japanese but still).