I tune my 7 guitar to drop B + low F#. I keep my 5 string bass in standard (BEADG). When things get into that F# zone I just play in the guitar octave and it sounds great... compensating in tightness and attack, where guitar tends to be a little looser and less clear (on guitar it takes great lengths to get great clear tone in extended range). I find coarse gritty distortion blended and aggressive attack on the bass can work well too. On bass I go to tactical lengths to get great, clear attacks on the B and other strings... using a lot of slapping and percussive fingerstyle to get the the right attack/punch factor in. In aggressive br00ts I find that one of the best roles of bass is in terms of punch and attack. On bass I cut my boomy lows (sub 100hz, which no one can hear/mainly muddies mix) and push low mids (180 hz), common method for cutting through heavy guitarists. My bandmix tone sounds overly aggressive almost harsh by itself but blended in mix it ends up just how I want it.