is bead on a 4 really worth it?

the guitarist in the band i'm trying to form insists on tuning to b w/his 6 string guitar. his seems to sound fine but my basses are 4 strings and i would have to use a 5 string set (minus g) plus do some work on the nut and bridge to make 'em fit. i could do this, but i have 2 fairly expensive basses (a stingray and a corvette) and i really don't feel comfortable making these kinds of modifications. i do understand that the lower tuning is really appropriate for the style of music we play (sludgy doom metal) but wouldn't drop d be enough? i also have my own 7 string guitar for song writing purposes, and i rarely see the need to play below d anyways. it's frustrating to have this kind of disagreement because we otherwise get along great and have identical goals for a band.