I play in a metal band in Manchester and use the B3k into a sansamp RBI live and a B7K into a sansamp bass driver in the rehearsal room / demoing. I've just spent the afternoon A / B ing the two setups and personally the I found the B7K into the bass driver the best overall.
For me, the B3K works best with the sansamp rather than on its own and although when I bought the B7K I thought it could replace both pedals, I've found that I prefer the extra oomph the sansamp gives me when paired with the B7K.
t's worth noting the EQ on the sansamp is flat with the drive at 10 o'clock and the blend as 12o'clock.