Before you go with flowmaster listen to mine, it has twin magnaflow mufflers and has a noticeable but not overstated rumble to it. Its very throaty from idle up to around 2700 then it gets quieter(resonator). And when you hit around 50 or so and OD kicks in you can barely hear it. Its perfect for cruising and when you open it the exhaust takes a step back so you can listen to the sweet whine.
. I'm not trying to sell you on magnaflow but we have similar setups and you may or may not want your like this I'm just throwing it out for you to chew on.
ANd I dont have a hi-flo cat yet but I'm pretty sure it will make my nice rumble a little more throaty. Dont have the aeroforce gauge either but its on my list when summer rolls around and I take care of my hazing headlight problem.