Thanks, Red. You folks are pointing out stuff of which I do not have a clue.
It's a deep rabbit hole. Bring your red pills.
My reasoning for a choice of 4x10 is this, starting with a specific history, and using a specific maker's cab as example.
JJ Burnel (Stranglers) started by using a guitar amp, and a guitar cab, for bass. He cranked up the high end to cut through the other sounds. The result became a mainstay of his and many other people's sound, but was not kind to the 12" drivers in his 4x12 cab. Later he had an 8x10 which fared better, but was inconvenient.
Years later, after many changes, he settled on an Ashdown ABM 4x10. These can be 4 or 8 ohms, it depends on the drivers and internal wiring detail which you get if you buy one. They have a single treble horn, with a switch for off/half/full horn output. He chose this for reasons that I took to mean it would work for guitar as well as bass, given how his sound originated.
There are many posts on TB saying that a guitar should have some high-pass filtering to make room for bass harmonics. This same method will reduce any bass-heavy sound when using a guitar through the Ashdown bass cab. Likewise, the treble horn's switch can easily remove nasty HF that makes the guitar sound more strident than you want.
If the cab is mounted on the floor, boundary effect will let it do a very good job for extended bass frequency response, and if you like bright hard-edged bass, switch the horn on. If you want guitar through it, use high-pass filtering, and switch the horn off.
This IS compromise, for sure, but it's CHEAP compromise, using existing signal-level gear and a horn switch, and it's likely to sound very good in this example because the cab was designed to support the kind of brightness usually wanted from a guitar, as well as for bass.
I'm sure other makers can satisfy this need, certainly Trace Elliott can, so part of the way to look for alternatives is to find out who chooses them for bright-sounding as well as hefty bass. That's a long list these days.

Specially for metal..