Probably either one will work. K&N uses the RC-4690 in their own CAI. It's about the same diameter, but almost 8" long. They also have a GenII CAI. The only difference I see with it is a shorter, oval tapered filter. I would guess it's better to go with the larger filter, if money and fitment is not a problem.
1995 325I, window tint, K&N, debaffled airbox, BMW #104 wheels, Nighthawk low beams, smoked side markers, smoked corners, smoked taillights, M3 stlye heated mirrors, various interior bits, Bosal cat-back.