I love it when people make comments like this.
OF COURSE the 6800NU and 6800GT are better than the two cards mentioned, but that wasn't the question. The question was: "6800LE or 6600GT. Which is the better performer? (AGP)". I'm making an assumption, but these two specific cards were probably listed because they are in the right price range, where a 6800NU or GT are not.
If a 6800NU or GT are in the budget, then definitely go for one of those as they will outperform either of the two original options by a significant margin. If not, they aren't an option and really aren't helpful recommendations.
At stock speeds, the 6800LE is a bit slower than the 6600GT since the LE is a significantly crippled 6800NU. However, MANY people have reported being able to unlock most if not all of the disabled pipes and shaders on the LE and then overclock to near 6800GT speeds. Of course, the 6600GT's also overclock pretty well, but won't come near the potential of a fully unlocked and overclocked 6800...
Out of the two options you mentioned, if your friend has no interest in trying to unlock and overclock the card at all, I would go with the 6600GT. If you feel adventurous and are willing to take a risk that it will not unlock fully (even if you can only get 4 of the 8 locked pipes unlocked and 1 of the 2 pixel shaders unlocked to get it to 6800NU specs, it will still probably match or beat the 6600GT in most applications) then I would go with the 6800LE.