<---also have a magnaflow 2-tip on 2.5" catback. The pipe bender who installed it did a really nice job of getting it tucked in the small area behind the rear axle and the bumper (it IS quite a lengthy muffler)
stock header etc...
When I first put it on, I almost had some buyers remose it was so loud....mainly because I don't want to be "that guy" at the local auto-xes with the stupid loud stock RS that sounds more like an exhaust leak...
..after about a year now, it had quieted down significantly, and I've actually gotten used to the sound.
yes, mileage went down and I also notice wild "mood" swings from one day to the next as far as driveability and feel; mostly dependent on the weather...
overall I am happy... I wouldn't like my car nearly as much back with the old stock quietness...