I guarantee you with my lack of skill, my attempt at using portable simd will exist while using manual intrinsics I doubt I'd get there.

The question for me is whether portable simd will result in faster code than plain auto-vectorisation; for the simplest loops auto has me beat (the few times I've tried it), but I imagine as the complexity grows I'll be more likely to try do something that breaks auto-vectorisation, and it'll be more obvious to me when I do that in portable simd.