I never aimed for 6cp rupture all the time, I use rupture at 5cp very often. Only for cd usage like exsang or snapshots I'm aiming for 6cp.
I did the calculations on excel (incl old vs new forumals of both rupture and ds). Rupture at 5cps is doing 15% more damage than before, Rupture at 6cps is doing 4.5% less damage than before. At the end the 5cp rupture buff negates the 6cp rupture nerf.
This is interesting, because the ds nerf is 5% already, but 6cp rupture dmg is actually only decreased by 4.5%. The rupture change buffers some of the nerf of ds.