COIL SPRINGS

HERES MY QUESTION TO ANYONE WITH KNOWLEDGE OF THIS SUBJECT.I HAVE A 1991 GT WITH A COIL-OVER SUSPENSION SET-UP ON FRONT.I INSTALLED THIS KIT SO I COULD LOWER THE CAR TO MY EXACT DESIRED HEIGHT.CAN ANYONE TELL ME(IN INCHES)HOW LOW A SET OF FOUR CYLINDER COIL SPRINGS ON THE BACK OF MY CAR WOULD DROP IT.IM MAINLY WANTING TO LOWER THE BACK FOR LOOKS AND FOR A SMOOTHER RIDE.IM NOT WORRIED ABOUT THE HANDLING(GOIN AROUND CURVES AT 100 MPH)AS MUCH AS I AM ABOUT THE RIDE QUALITY.THANKS GUYS AND GALS
 
My car has 4 cylinder springs all around. The rear doesn't sit much lower than a fox with stock V8 springs. Because unlike the front where the V8 weighs much more. The rear on a 5.0 and 4 banger car is roughly the same.
 
ALRIGHT THEN,THANKS MAN.GUESS ILL JUST BUY SOME AFTERMARKET CONTROL ARMS WITH THE ADJUSTABLE SPRING PERCH TP LOWER THE BACK,BUT I WAS TRYIN TO SOFTEN THE RIDE A TAD BIT ALSO.YOU KNOW ANYTHING ABOUT THE REAR SPRING RATE OF THE 91 GT VERSUS LETS SAY A 93 COBRA REAR SPRING .I HEARD THEY MAY BE A SOFTER RATE THAN MY 91 MODEL BUT I HAVE NO EXPERIENCE WITH THE ISSUE