Sway Bars

Yea you will get alot of mixed opinions on this one but I use them (steeda) and the diffrence is night/day......jj

The difference is night and day, but they are kind of overkill on a street only car. Dont get me wrong they make the car handle better in some conditions, but everyday road manners will deteriorate noticably, depending on how rough the roads are in your area you might hate them. Your car wont soak up the real big bumps anymore, you will. (Although you probably wouldnt notice this at first because you would be ripping your car around the corners enjoying the perceived improvement because there is less body lean, and improved turn in) I live in O.C. and we have a mix of great roads and horrible roads, the thicker bars feels great on the smooth roads, but more often then not, the roads are not super smooth. The car rides better, turns more evenly, and produces higher mph's in turns with the stockers. The thicker bars can make the ride a little twitchy. And will likely create a understeer or oversteer contidion at low or high speeds depending on the setup.
Keep the stock swaybars. Ford went through alot of work to create some balance with the chassis., Some random swaybar kit will not not help I'm sure Eibach et al didnt spend millions like Ford in R&D and the results speak for themself. I have been in Suspension Parts Denial before(many time tinny) that is why I can type this.

The Eibach sway bar kit is kind of stiff. If I remember correctly the Eibach front bar is 36mm vs the stock 26.5. If you just want to go slightly stiffer you could go with the Cobra bar up front which is 28mm and the V6 bar which is 21mm vs the stock 23mm out back. This is the setup the Bullitt has. Most who have driven a Bullit and a standard GT will tell you the Bullitt handles much better than a stock GT.

I have the upgraded Steeda ones, front & rear. I could tell a big difference and I already had springs & subframes.

I have them, they're great

Think of swaybars more as suspension 'tuning' parts rather than just a straight upgrade. On a stock mustang where the suspension understeers, a stiffer rear swaybar would help make the car more neutral, but a new front swaybar would be unnecessary. I would recommend that you do all the suspension upgrades that you are going to do, and then do swaybars last, because the perfect swaybar combo for a stock mustang will be different than the perfect swaybar combo for a mustang with x suspension upgrades which will also be different than the perfect swaybar combo for a mustang with y suspension upgrades.

I installed the Eibach sway bars and all I have to say is

the difference the front sway bar made alone was huge, car handles totally different. Definitly go for it, you will not be disapointed