As I have been saying in almost every post in this thread so far is that every amp setup and mix will be different, which is why I don't look at arbitrary numbers, and in my opinion any number is arbitrary because the more you fall into that habit, the more you are mixing by numbers. Personally I like to set the most shallow slop possible on my eq and then start dragging the low pass until all the aliasing unmusical noise disappears, then I try to add a small boost right before the cutoff frequency of that low pass and I will move is around to see where it is most effective for that tone.
I know what you mean though, the last big tone shootout that I did I found the guitars to be extremely dark in the mix. In terms of the LPF, all I had to go down to was about 14K when all the noise went away. It still needed a presence though, which I boosted at about 7K, anything lower, like 5-6K while sounding good, made the low end of the entire mix sound extremely boxy and wooly, making the bass and the extreme low mids out of control. And even though I have those settings where they were the resultant mix still had really dark guitars, about as dark as the Nickleback YT video Ermin posted.