Objective measurements include pretty much anything the auto magazines do. Motor Trend, Road & Track, Automobile, etc... Usually includes skidpad, figure 8, some sort of slalom, a lane change maneuver, time around a race track, and some others.
Subjective measurements usually include things like willingness to change direction, steering feel, perceived body roll/cornering flatness, etc..
My guess that the Performance version will have different springs/dampers and anti-roll bars (ARBs) - stiffer - to better compliment/take advantage of the Michelin Pilot Sport 4S tires. Could also include other things like revised suspension uprights with bigger bearing assemblies, beefier steering components and suspension links/bushings, bigger half-shafts, stiffer mounting bushings for front and rear suspension subframes, and/or many other things.