The Iroc was the top dog, then the z28, then the RS, then the base car. The iroc's had the the highest hp, biggest rims (16x8) etc plus a slightly different ground effects package. I think the difference between the Iroc and z28 could be compared to a 4th gen SS and a 4th gen z28. The z28 which I believe was killed after 87 did not have the big tires or as much hp. The Iroc option was dropped in 92 I believe and then the z28 was the top car again. The RS was just an appearance package. You could get a v6 RS or v8 Rs.
1969 Camaro 350, Trickflow heads, ST-10 4spd, Hotchkis suspension, Baer SS brake kit, moser 12bolt