Iray emissive map v. material zones (high poly) - which is more efficient?

Silent Winter

Imagine I've got a sphere (reasonably high-res to look like a sphere in close-up with smoothing on) and I want a single line around the equator to glow.

Would it be better to use an emissive map (at 4096x4096) or to set a ring of polys as a separate material and set that to emissive.

With the latter there would be a lot of polys, each being its own emissive plane, but would using a map instead make a difference?