[elektronaut]

For the low B on my 7 string, I get better intonation and tuning results by using power chords up and down the neck with distortion on rather than relying on a tuner. Fretting tension and picking intensity becomes a huge factor with low tension and high string gauges.

[SwellJoe]

Yeah, tuning in fifths makes sense because you're playing in fifths. It also lets you bring it up into a register you can hear clearly (and the beating will be audible even in the lower registers, especially with distortion). The short scale of a guitar makes going really low challenging, and you'll have more of the sharpening due to heavy picking.

When I played metal and tuned the whole guitar down to D or C# (this was before 7 strings were really a thing), I still used the stacked fourths and fifths method of tuning and it worked for that, too. Since you can strum at normal playing intensity when tuning this way, you can accommodate whatever you're normal playing style is.