Spanards attach their pray differently to GT's.
A GT will come up behind and swallow the bait.
A Spanard or any other type of Mackeral comes up beside the bait and smashes sideways to catch their pray.
I have always found RMG 150 3.5M in triple stripe, Orange head, with Yellow under the head, Purple in the middle and Pink Tail to be the most effective. I put a Good Treble on the tail, and 2 single Gamakatsu "Live Bait" 8/0 on the front hook eye and leave the middle eye with no hooks.
The singles sit proud of the body unlike trebles that only the bottom hook is proud. Any Mackeral that swipes at the RMG gets hooked.
I have also had good luck with a Laser Pro 170mm Blue 2M with Blue and tiger stripes on the top, silver on the sides and yellow belly.
When I have both out trolling. the hookup rate is 2 to 1 RMG to Halco Laser Pro.
I had just caught a Mackeral once and the boat was stopped, I had the RMG floating in the water beside me and I noticed a shadow underneath it. I kept still and watched a Spanyard float up beside the RMG, swipe sideways at it and had a hook up of a 10kg fish. It was at Lee Point in Darwin about 6 years ago.
Mark