BMR is close by me, so I went over to their site and talked to Kelly (their Mustang guy) first hand. I didn't talk about a comparison between Steeda and BMR, but both are high quality. You definitely can't go wrong with either. That being said, I took a ride in a buddies 14 with a full BMR Suspension kit, and it felt like a completely different car than stock. They say (BMR) that a 15 GT with their springs and sway bars will run laps around a boss 302. I ended up getting their cradle lockout kit and sway bars. Haven't installed them yet though....
2000 Mustang GT-Former giggle gas addict
1990 Mustang GT w/ Vortech V3
***resident gun idiot***