RS 4-2 is a "sporty" street pad good enough for some spirited driving but not on too heavy cars or for circuit racing. Pagid recommends them as a rear pad on track-day cars, along with better gripping pads on front. Had them on my car and replaced them with RS29 and later RSL1. I've had RS29 on both my Polo 6R GTI (standard brakes) and Golf GTI (Ap Racing Pro5000+ brakes). The Polo is my daily commute so I've only had few situations of hard braking from high speed. Of course, immediately after those, brake judder appeared as the brakes weren't heated up prior to those emergency brakes. Same pad on my track Golf were perfect every time. Although the braking was much harder, the pads were always heated up before each session. I don't know how much of a influence was due to the braking system itself but putting some heat into the pads before hard braking is definitely a must.
