6800 is faster in about every situation, especially with FSAA and AF where memory bandwidth is truly required, or just in games that hog bandwidth.
People above seem to mix 6800 with 6800LE, which is same speed with 6600GT, but faster with high bandwidth situations and FSAA+AF settings.
People above seem to mix 6800 with 6800LE, which is same speed with 6600GT, but faster with high bandwidth situations and FSAA+AF settings.