i asked a buddy of mine the same question cause i'm in search of a tranny to put on my b1 for my dd, he explained it that the gsr would be better because a b16 tranny is geared for the better torque at low rpm's and the b16 typically revs higher than the b18, as to where the gsr has the shorter gears for higher rpm torque and don't rev as high, specially the b1, it has a 7200 redline on a factory tune, i had a gsr on a b1 before and it pulled great so thats what i'm going to go with again, if that makes any sense at all? i don't like to think i know it all so, i hope i didn't get that backwards, end result, i've heard more better things about a gsr tranny on a b1 than a b16 tranny