Affinity is based on the SA, which usually performs pretty well on all platforms. Pierce employs a recombinant SA that features improved pH profile for added flexibility in protein isolation. They have high capacity, but that may not be important for you.

Specificity is more related to the bead composition. And all magnetic beads are fairly sticky.

MagnaBind beads are silylated. This helps them achieve lower background, but with some loss of sensitivity.

When you say you want low non-specific binding, I think you really only care about stray oligos. Quantitatively, that should not be a problem, although you may need to add a little heat to melt weak duplexes. Qualitatively, you should expect to see a small amount of irrelevant oligos, detectable via endpoint PCR.

If you need to minimize protein carry-over, I suggest you an anti-biotin antibody for pull-down, instead of SA.