Control Arms

there are few companys that will provide you MUCH better than stock control arms for a good price. You could go with MAC, Granatellis or another cheap, but effective company that will help you gain some traction.
 
I know that they sell Uppers and lowers for like $219. you could buy that then resell the uppers since you already have some. They are good, but there is going to be better out there though.
I would go with GMS and their "weight jacker" lowers though.
 
Use the steeda lightweight lowers, fair price at about $200, and they are of nice quality.
If i was in the market for a new set, i'd definetely use the steeda weight jackers, but the cost of them is very high.
MM's are good too.
I'm anti mac products, so i wouldn't use them.
 
I think the overall answer to your question is that any aftermarket controll arm has to beat the stockers by a longshot. The crappy stamped steel junk with by now rotted/worn out bushings. You can bend them by hand with the car lifted by pushing on the axel. Even some MAC's would probally make a world of difference. If I were to buy another mustang, they would probally be one of the first things I would do to it because the stock unpredictablity is downright scary. Don't forget the axel bushings.