I can tell a difference when lopassing at 8K, personally.
I prefer lopassing at 12K, higher, or not lopassing at all. Guitars don't have a lot going on there, true, but they got so little that I don't find it problematic to fit with the cymbals. And what little they got adds to the 3D-ness and airiness of the guitars (to my ears). That is especially true if you like to add some tape saturation or some sort harmonic enhancer later down the line to your guitar or master bus.
But it also depends on what aesthetic you're going for. I do tend to prefer bigger/wider guitar tones. I also mix Melodic Death Metal. Aesthetics for other genres are certainly different.
Also would like to add that guitar tone is more than just fundamental frequencies. There is a bunch of harmonics going on at all times, especially with distorted guitars.
Also, many people on forums try to force on you the notion that "d00d u n33d midz to cut thru da mix" and frown upon running amps' mid knobs low and/or EQ pedals (or buses when mixing) doing some shapintg to the mids. Not always, but often, it's people with zero experience with a mixing board or a DAW. My point is don't be afraid to scoop some mids. I understand you might not be going for an 80's Metallica aesthetic, but cutting the right areas in the mids usually makes your guitars sit in a mix better, feel clearer and more up-front, and let the rest of the instruments breathe better. Just be tasteful with how much and what mids you cut. Remember that guitars aren't the only instrument in the mix too, so you don't want them sitting on top of everything either.
JMO/JME.