shenayim mikra or pesukei d'zima -- which takes precedence

The Baal haTurim has a cute remez on the first pasuk of the parsha about the importance of shenayim mikra v'echad targum (=Shmot).

An interesting question that was posed to R' Shach: l'chatchila shenayim mikra is supposed to be done before seudas shabbos.  When R' Shmuel David Munk, who went on to become Av Beis Din in Haifa, was a bachur in the yeshiva he was behind in shenayim mikra, and because of scheduling, would not have time to finish before the seudah.  He asked whether it would it be better for him to skip pesukei d'zima (except for maybe ashrei and nishmas) and do shenayim mikra in the time gained since m'dina d'gemara most of pesukei d'zima is not obligatory but shenayim mikra is, or should he not change the tzurah of tefilah?

R' Shach paskened that shenayim mikra takes precedence; the Chazon Ish disagreed.  (see here and here #129)