The primary penalty is likely outputting the polylines. If you wrap them in Grasshopper.Kernel.Types.GH_Curve you should see a substantial performance boost. And you need to compile the component to really see the benefit of writing this in C#. Here’s going to 1000 with the GHPython example I posted, it’s slightly faster in SDK mode. I would expect a non-threaded C# scripting component to at least hit this performance:
230824_GetFaceLoops_01.gh (7.3 KB)