IMO you do not need anything real fancy. Maybe a few 36" t8 strips with a 6500k bulb.. That's what I'm using in my silver tank.. Lights up the tank pretty well
I use the Marineland Double Bright LED and it seems to be too bright for my Silver. Aro is more active when it's off or when only the blue/moon light is on.
If you want LED, maybe go with the Marineland Single Bright LED. Otherwise, T8 strips should be ok.
I believe I read that the shorter lights (36"-48") provide the arowana a kind of refuge when you use them on a 72" tank. Leaving the corners dark gives them a place to relax when the lights are on. It also creates a cool lighting effect (well, some consider it cool). I'm currently using a 48" on my 72" tank, which I am currently cycling for my future Jardini.