As you can tell, 2 chamber flowmasters are like buttholes. There is NOTHING wrong with that, but I prefer to be the odd-ball on the block. Every mustang in my "hood" has 2ch flows...
I ran a dynomax ultraflo 2.5" cat back sytem with a mac power chamber and dynomax equal length shorties. This produced a relatively mellow idle tone; however, when you stick your foot to the floor it sounds wicked (kinda like vroom, vroom
). No interior drone like the flow's - and I too was complimented on how "unique" it sounded. I later removed the tailpipes and welded 3" turn downs on and THAT eliminated the mellow idle tone. It sounded even more wicked...
Try something different...
I now run magnaflow mufflers with turndowns (same as an ultraflo on the inside with the difference being the welded on end caps and fully polished) The dynomax mufflers have the rolled seams (not quite the quality as the magnaflows)
My family's exhaust shop that I work at carry/stock flowmasters and we also have the magnaflow products available for order...
I have installed three cat back kits on a Cobra, a GT with a Cobra rear valence, and an LX... That is, it was the kit with the polished 3" tailpipes, I haven't done/sold any with the GT style tp's. Very impressive sounding even with stock manifolds/headers and the factory cat h-pipe. Mellow idle tone and all the performance exhaust rumble you need at WOT
Ultimately it's up to you of course, just discussing options...
I have installed a Bassani cat-back kit on a mildly modded stang that sounded good too, and the tp's (LX-Cobra) have a removable resonator/silencer.
Both kits are around 500 bills (Bassani is fully stainless, the Magnaflow kits are aluminized with stainless muffs and tp's, and the Flowmaster kits {a bit cheaper last I checked} are fully aluminized (LX kits are available with the stainless tp's)
I have installed more flowmaster mufflers on mustangs and done custom duals with flows on trucks/street rods than imaginable...
I prefer the sound of the three chamber for mostly street vehicles, to give you an idea where I stand on preference issues. The two chamber is LOUD (if that's what you're going for, get the two chamber flow's). Three chambers are kinda quiet with stock h-pipe's and sound really good with and off-road pipe. Very good with turndowns...
Decisons-decisions to make... (whew that was a long post)