Coilovers
I had some Bilstein coilover shocks on my MK1 Renault 5. The firmer springs do help control body roll and sharpen the steering, but my panel beater noticed cracking through the body. Remember that the R5 is a monocoque and not a platform chassis. I would be hesitant about using coilovers on a R4 and I would suggest thicker (and a rear) anti-roll bar if body roll is the main concern.
Too much stiffness in the "bump" will upset the cushion-like damping of the R4 for which it is renowned. Most of the suspension control comes through the firm "rebound" of the dampers. It is a typically French ride quality built into their cars to deal with cobblestones in urban areas and the lack of proper roads in North Africa where most of the French colonies were located.
David