No offence james, but an EA 3SPEED with a 2.5" redback muffler with hotdog resonator will drone on the freeway.
That's the EXACT system that I have and it drones only on the freeway. Only because my exhaust hits it's highest DB levels at 2400rpm, exactly the same RPM that I sit on when driving on the freeway. Obviously this isn't going to happen with your XR6 as you've got a 4speed, so you'll be cruising on or around 1600-1800rpm at 100-110kph? (correct me if i'm wrong) So with the DB levels reaching their peak at around 2500rpm, your won't get any real drone in your cabin with a 2.5" 1 hotdog, 1 muffler system.
However, driving around town and driving up to 85kph my three speed doesn't drone at all only on the freeway.
Personally, I would go a 2.5" Mandrel Bent (stainless if you can afford it) zorst, with a muffler and a hotdog resonator. I'd also recommend going Lukey, as they have a good reputation for sound when applied with a Ford 6.
Also, get em to check your cat since their down there. You might need to replace it, to take full advantage of your new zorst. But I wouldn't go a "hi-flow" cat, as they are a crock of shit and don't improve performance at all. Just go a standard 2.5" cat..