I've had 85's with speaker seats, an 87 without speaker seats but with B pillar speakers, then I installed speaker seats and wired them into the B pillar harness. Each system has its own sound qualities. I like the current 8-speaker system I have with the speaker seats and B pillar speakers.
With just speaker seats, there's reasonable separation coming from the seats. When wired into the B pillar speakers, you lose some of the ambience from the seats, but the overall separation is still good. I like to use The Beatles Sgt. Peppers album as a test because it has great stereo separation.