Top speed on a highway or high mountain roads has little to do with track driving.
As you stated "The Z handles it great." and doesn't need much help being a good driving car. You want to make the Z into a 911 it's going to cost a lot and/or sacrifice a lot. The most significant upgrade all around not knowing "Well, are you using this for street or track? What kind of track driving are you doing? Well, in that case, I would go with x,y,z." would be bigger better tires.
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GTR TT 493Whp/431lbft, Ecutek, Southbend 6puck,Quaife, RPM RollBar 4Point, R888R, JRZ RSPro F(10R/10C) R(10R/6C) 1000f500r inlbs+150inlbs Tender, SPL everywhere. Full Specs
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