Tried -2000 ft and +0.4 M, as well -4000 ft and +0.2M.
I'd take the second option straight next time. The change was noticeable and quick, let's say 10 minutes.
-2000 AND +0.2 was good enough to stabilize the temperature, without discernable improvement. Doing only one of them was not convincing.
-64 SAT and -41 OUTR TK on A1 grade. Inners -37 and that was the root of it.
Another nasty was the low tropopause with -64 well below the original FL, we got limited by environmental envelope during descent!