Doug, first I assume you are talking about Giant Trevally?
The BS of the leader depends on the size of the mainline you are using. I guess you average fisherman (were there such a thing) who lures for GTs would use a PE8 mainline with a leader anywhere between 150 and 250 lbs. In areas where the GTs are on the smaller size you will find people using PE5 and PE6, and there are plenty of folks who use PE10 and even PE12 for larger fish.
On wire leaders - I will not use wire for any fish as it dries up your bite rate, sometimes to nothing.
