If your going to synth these what you should do is do one sitting of synthing and then grab a few stacks of lightning crystals and desynth.
You'll be better of with getting either Silk Thread or Darksteel Ingots
by the by.. if you find yourself short on ingots you could always visit the NPC and sit and desynth these for gil ^.^
I know on Siren it's 500-700k a stack for ingots.. so this is a good way to make a little gil..