You won't notice much. Maybe .05-.1 TOPS! IMO when I was looking for a K-member I looked for strength (so if I wrecked I wouldn't have a motor in my lap) and handling first, THEN weight savings (why i chose max motors! My second choice was PA racing).
you will see gains with the whole kmember and coilover kit. My buddies Mach run 7.80s with prostars biggies and skinnys on et streets. But he never run it before he done all the work. Went 7.30s with a 75 shot spinning hard. Then he broke the rear upper control arm. They were upr's prostreet's that broke at the welds. BTW this is in the 1/8th mile.
It's more of a weight balancing thing than a weight removal thing... yeah A-arms and such are nice, but it's nicer getting closer to an ideal balance for 1/4 and open track