True F-1 Simi-Angus cows (nothing else in them) make some of best show steer producing mommas and feedlot calves from a commercial standpoint. From a commercial standpoint, it depends on what your buyer wants as to what bulls you use on them. More often than not, any kind of halfblood exotic-angus bull will give you calves that will predictably grade choice with a YG 1-2.
More often than not environmental and management differences overwhelm genetic variation from calf to calf on a producer-size scale from these kinds of crosses relative to breeding purebred to purebred.
From a show steer standpoint, the Simi-Angus momma gives the calves the necessary growth, soundness, and size while the sire (i.e. Heat Wave bloodlines) give them the muscle shape, bone, depth, and hair.