If it was me the difference between getting the 600,01,02 for surround use may be largely determined by the space you have relative to the size of the speakers. I wouldn't go with the 600's over the 601's if you have room for the 601s... and so forth with the 602's... if you have room for them, I'd go with the larger ones considering the 3 models. I have listened to all 3, and the 600's are nice, but again, if the room is available, I'd go with the larger 601's or 2's.
What are your feelings about the surround model in B&W's 600 series? DS6 S3? I haven't auditioned them (or I didn't pay attention if they were there, I was looking at bookshelf mains), but I personally like dipolar or bipolar surrounds vs the regular 600 or 601s... but you said you don't have a back wall and only a half wall on the left side, so I don't know how exactly you will be placing the speakers... If the DS6 S3 speakers would work positionwise, I'd consider them. Being dipolar or monopolar configurable, they give you the option of chosing what you like best, and if the speakers are going to be 4 feet away, they may be more diffuse sounding than the direct front firing models.
Brad