I've now got all 4 spara units completed for the Early Persian Army though the I do intend to do a 'new' Saka unit. I went with red because I liked both the red and blue Immortal elements, will only use 1 of them in this army, and prefer the blue unit.
Of the robed figure conversions I think the Persians are far less successful than the Immortals or Medes. The head coming from a smaller and earlier figure in the PE Range it doesn't quite fit correctly.
I think I may also need to touch a few figures up, especially the back of the standard.
I think the front view tends to show the awkward angle a couple of the heads are at. Still, they do the job.