I'll share my experiences here.
Focusing on handling and street. I dont care much about drag racing anymore.
I've had both setups on my cars. My old car (the old Vibrant Red) received the complete GR40 Super Street Kit, but before that it had the Eibach ProStreet coilovers kit and sway bars. My new car, I decided to go with an IRS.
However, the 4 link will be absolutely fine for the majority. For MY liking it sucks. Blame riding in and driving cars like Gen 2 Vipers and Corvettes and 3rd/4th gen Fbodies for that.
Again, this is MY opinion on having all 3 setups on a Mustang. Modified 4 link vs TA/PHB and now IRS.
Just a quick description on my 3 setups and components used:
Setup 1:
95 Vibrant Red Fobra
8.8 SRA
Eibach ProStreet CoilOvers= F: 200LB coil over spring over an Eibach Strut R: Stock location 250LB spring (Eibach Sportline rear springs are a 250lb spring as well) with Eibach shocks. These are the spring rates that come with the Eibach kit.
Eibach Sway Bars F and R
Prothane Short End links (for front swaybar)
MM FL Subframes
Strut Brace and MM K member brace along with Prothane A-arm bushings and C/C plates.
Lakewood 20150 LCAs
Stock UCAs
17x9 Cobra R reps, 255/40 up front and 275/40 in the rear.
Compared to Stock, BIG difference in handling and ride quality (not a jarring ride at all, as one would expect from a lowered mustang, BUT having a matched spring and damper combo is KEY).
Under agressive cornering situations you could feel the rear end would be on the verge of wanting to slide out from under you.
However, for the majority of us this setup (or something similar) would be just great and left there.
Setup 2:
95 Vibrant Red Fobra
Griggs Racing GR40 Super Street Kit, upgraded the control arms (to bodyside hiem joint style) and the rear shocks (from the Street valved shock to their Track 1 shock)
http://www.griggsracing.com/product_info.php?cPath=4332_4310_4347_1060&products_id=555
So Panhard, torque Arm etc etc (all the components described in that link)
Spring Rates= Front: 350 lb. Rear: 250LB
Using the Eibach Swaybars.
17x9 Cobra R reps, 255/40 up front and 275/40 in the rear.
Compared to setup 1, what a difference in handling. It was like driving a completely different car, night and day). None of that feeling that the rear end wants to get out from under you. Street ride quality was the same as Setup 1. And the rear end felt positive going over bumpy roads etc.
Setup 3:
95 CW Cobra.
After a situation that happend at home in my garage, that involved some body damage to Vibrant Red that I didnt feel like spending the money to fix/bodywork and paint. I bought CW and proceeded part Vibrant Red out. I kept the 306 and T5 transmission and the front suspension pieces to install into CW. The rear GR40 Griggs suspension and SRA was sold off, along with the SRA from this CW Cobra.
I picked up an 03 IRS for a wicked deal and used the money saved (from paying the going rates of 03-04 IRS setups $1,000+) and bought the FTBR FT5000 Bushing kit.
Front =
GR40 C/C plates, Koni Yellows Single Adjustable struts, 350lb CO spring, Eibach Sway Bar, FRPP STB, MM 4point K-member brace, Prothane A-arm bushings, Short swaybar links, 03 Cobra steering rack and MM steering shaft.
Rear=
03 IRS, FTBR bushing Kit, Koni Yellow SA shocks, 550lb coilover springs, Eibach Swaybar, MM adjustable endlinks, billet flow IRS brace.
17x9 Cobra R reps, 255/40 up front
17x10.5 Cobra R reps, 285/40 out rear.
Street ride quality with the IRS, better than both the SRA setups. Agressive handling , this IRS setup is comparable to Setup 2 (TA and PHB).
Conclusion:
I cant decide an overall winner between IRS and an SRA with a TA and PHB, as there are Pros and Cons between each (read MMs link when they discuss the IRS vs SRA with TA and PHB and the points they give). So I'll give them a TIE
.