Lear, seeing your mention of the Eibach springs reminded me of another handling related point. The R/T comes stock with all season tires, and not very super all season tires (Goodyear and Michelin are big names, but the actual tires they provide are old designs that are no better than average). The hotter models of mustang and camaro come with pirelli P-Zeros, which are bada** summer-only performance tires, hotter than even the Goodyears that come on the SRT-8 Challenger.
For what a difference they make, see p46 of the February Car and Driver talking about the difference they make on the Mustang:
"Once the P Zeros arrived, though, we would have believed that the entire suspension had been overhauled. There was noticeably more grip everywhere, leading to lap times that were worlds-more than five seconds-quicker [around VIR]."