All things being equal, a straight grade oil will be more shear stable than a multi-grade.
As for pour point, it depends on the grade and the quality of the base oil. Amsoil's straight 30 wt made from PAO has a very low pour point. A typical mineral based 30 wt may have what appears to be a low pour point, but its cold cranking viscosity will be very, very high. Back when auto makers would list straight grades in the owners manual as well as multi-grades, 32F was usually listed as the lowest temp in which 30 wt should be used. Colder than that, and you'd go to 20w or 10w or 5w straight grades, depending how cold you expected it to be before the next oil change.