I think I would go with the SSP for sure. Another thing I don't see mentioned in this thread is the 86's have smaller front rotors.
Here's a list of what made them special. I think some of it is slightly inaccurate, but it's pretty close. For example, I think the Hypereutectic Pistons started in 92 rather than 93.
* Engine, 5.0 L HO V8 with Sequential Multi-Port Injection
* Forged pistons, roller cam (Hypereutectic pistons 1993)
* Engine oil cooler
* Aircraft-type silicone radiator hoses and clamps
* 5-speed manual or 4-speed AOD transmission
* Auto transmission fluid cooler
* Brakes, power disc front/drum rear with rotor shields
* Stainless steel factory headers
* Dual exhaust system w/stainless tips
* Fuel tank capacity — 15.4 U.S. gallons (58 L)
* Heavy duty stabilizer bars, front and rear
* Full instrumentation with in-dash tachometer
* 130 and 135 amp internally and externally regulated heavy duty alternators
* 2 Piece VASCAR speedometer cable
* Certified calibrated speedometer 0-140 mph(1982-early 1989) and 0-160 mph (late 1989-1993)
* Non-operational courtesy lights (safety feature)
* Relocated rear deck release
* Single key locking doors/trunk
* Reinforced floor pans
* Full size spare tire
* 15" X 7" cast aluminum wheels
Sourced from:
http://en.wikipedia.org/wiki/Ford_Mustang_SSP